问答题Practice 1　　The greenhouse effect causes trouble by raising the temperature of the planet. The 1 rise is not very much，but the Earth’s ecosystem is very weak，and small changes can have large effects.　　It has been believed that this 2 of one degree

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

Algae are plants that can__________.
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A．live in very hot temperatures
B．live in very cold temperatures
C．manufacture oxygen
D．all of the above

共用题干
Lakes,Too,Feel Global Warming

There's no doubt:In the last few decades,the average temperature on Earth has been higher than it has
been in hundreds of years.Around the world,people are starting to measure the effects of global warming一
and trying to figure out what to do about it.
Scientists recently used satellites to study the temperatures of lakes around the world,and they found
that lakes are heating up.Between 1985 and 2009,satellites recorded the nighttime temperatures of the sur-
faces of 167 lakes.During those 24 years,the lakes got warmer by an average of about 0.045 degree
Celsius per year.
In some places,lakes have been warming by as much as 0.10 degree Celsius per year. At that rate,a
lake may warm by a full degree Celsius in just 10 years.That difference may seem small一you might not
even notice it in your bath.But in a lake,slightly warmer temperatures could mean more algae（水藻）,and
algae can make the lake poisonous to fish.
The study shows that in some regions,lakes are warming faster than the air around them.This is impor-
tant because scientists often use measurements of air temperature to study how Earth is warming. By using
lake temperatures as well,scientists can get a better picture of global warming. The scientists say data on
lakes give scientists a new way to measure the impact of climate change around the world.
That's going to be useful,since no country is too big or too small to ignore climate change.Scientists
aren't the only ones concerned.Everyone who lives on Earth is going to be affected by the rapid warming of
the planet. Many world leaders believe we might be able to do something about it,especially by reducing the
amount of greenhouse（温室）gases we put into the air.
That's why the United Nations started the Framework Convention on Climate Change,or UNFCCC.
Every year the convention meets,and representatives from countries around the world gather to talk about
climate change and discuss global solutions to the challenges of a warming world.

Lakes seem to be warming faster in Asia.
A:Right
B:Wrong
C:Not mentioned

共用题干
第二篇
Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO₂).Car emissions are a major problem, but the truth is that more CO₂ comes from the energy used at home.The average household creates around
five and a half tonnes of CO₂ a year,and it is the same CO₂ that is changing the climate and damaging the environment.
CO₂ and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO₂ and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.
In 2008,the total UK CO₂ emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO₂ emissions.These figures show that a significant amount of CO₂ results from ordinary citizens carbon footprint in their daily activities and lifestyle.
The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．

CO₂ emissions from vehicles_______.
A:are a more serious problem than energy shortage
B:do not cause any problems
C:are high because the average household owns a car
D:contribute considerably to greenhouse gases

共用题干
第二篇
Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO₂).Car emissions are a major problem, but the truth is that more CO₂ comes from the energy used at home.The average household creates around
five and a half tonnes of CO₂ a year,and it is the same CO₂ that is changing the climate and damaging the environment.
CO₂ and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO₂ and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.
In 2008,the total UK CO₂ emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO₂ emissions.These figures show that a significant amount of CO₂ results from ordinary citizens carbon footprint in their daily activities and lifestyle.
The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．

Which of the following is the best title for the passage?
A:Ways of reducing the UK's CO₂ emissions.
B:UK citizen's carbon footprint.
C:The effect of industry on climate change in the UK.
D:Changes in weather patterns in the UK.

共用题干
第二篇
Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO₂).Car emissions are a major problem, but the truth is that more CO₂ comes from the energy used at home.The average household creates around
five and a half tonnes of CO₂ a year,and it is the same CO₂ that is changing the climate and damaging the environment.
CO₂ and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO₂ and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.
In 2008,the total UK CO₂ emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO₂ emissions.These figures show that a significant amount of CO₂ results from ordinary citizens carbon footprint in their daily activities and lifestyle.
The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．

The results of climate change in the UK can be seen in______.
A:cooler summers
B:water supply
C:warmer winters
D:stronger winds

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To Survive or to Vanish

1.Over 3.6 billion years ago,the first creature was born in the world.Since then,the earth started its era with life.The history of life on earth has been a history of interaction between living things and their surroundings.To a large extent,the physical form and the habits of the earth's vegetation and its animal life have been molded by the environment. Considering the whole span of earthly time,the opposite effect,in which life actually modifies its surroundings,has been relatively slight. Only in the present century has one species一man acquired significant power to alter the nature of his world.
2.During the past 25 years,this power has not only become increasingly great but it has changed in character. The most alarming of all man's assaults upon the environment is the contamination of air,earth,rivers,and sea with dangerous and even lethal materials. This pollution is for the most part irrecoverable.In this now universal contamination of the environment,chemicals are the sinister partners of radiation in changing the very nature of the world the very nature of its life. Chemicals sprayed on croplands or forests or gardens lie long in soil,entering into living organisms, passing from one to another in a chain of poisoning and death.Or they pass mysteriously by underground streams until they emerge and combine into new forms that kill vegetation,sicken cattle,and work unknown harm on those who drink from once pure wells."Man can hardly even recognize the devils of his own creation,"as a scientist has said.
3.Hundreds of millions of years have passed before the globe produced the life that now inhabits the earth.Given time not in years but in millennia life adjusts,and a balance has been reached.But in the modern world there is no time.
4.The quick steps of change follows the impetuous pace of man rather than the deliberate pace of nature.Radiation is now the unnatural creation of man's tampering with the atom.The chemicals are the synthetic creations of man's inventive mind,having no counterparts in nature.
5.To survive these chemicals would require not merely the years of one man's life but the life of generations.And even this,were it by some miracle possible,would be futile,for the new chemicals come from our laboratories in an endless stream;almost five hundred annually find their way into actual use in the United States alone.Among them are many that are used in man's war against nature.Since the mid l940's over 200 basic chemicals have been created for use in killing insects,weeds,and other organisms described as"pests".
6.It is not my contention that chemical insecticides must never he used.I do contend that we have put poisonous and biologically potent chemicals indiscriminately into the hands of persons largely or wholly ignorant of their potentials for harm. We have subjected enormous numbers of people to contact with these poisons,without their consent and often without their knowledge.I contend,furthermore,that we have allowed these chemicals to be used with little or no advance investigation of their effect on soil,water,wildlife,and man himself. Future generations are unlikely to forgive our lack of concern for the integrity of the natural world that supports all life.

The effect of life modifying its surroundings has been_______.
A:man's tampering with the atom
B:enormous numbers of people to contact with these poisons
C:the integrity of the natural world that supports all life
D:inventive
E:irrecoverable
F:relatively slight

共用题干
Some Things We Know About Language
Many things about language are a mystery,and many will always remain so.But some things we do know.
First,we know that all human beings have a language of some sort. There is no race of men anywhere on earth so backward that it has no language,no set of speech sounds by which the people communicate with one another. Furthermore,in historical times,there has never been a race of men without a language.
Second,there is no such thing as a primitive language.There are many people whose cultures are undeveloped,who are,as we say,uncivilized,but the languages they speak are not primitive .In all known languages we can see complexities that must have been tens of thousands of years in developing.
This has not always been well understood;indeed,the direct contrary has often been stated.
Popular ideas of the language of the American Indians will illustrate.Many people have supposed that the Indians communicated in a very primitive system of noises.Study has proved this to be nonsense .There are,or were,hundreds of American Indian languages,and all of them turn out to be very complicated and very old.They are certainly different from the languages that most of us are familiar with,but they are no more primitive than English and Greek.
A third thing we know about language is that all languages are perfectly adequate. That is, each one is a perfect means of expressing the culture of the people who speak the language.
Finally,we know that language changes.It is natural and normal for language to change;the only languages which do not change are the dead ones.This is easy to understand if we look backward in time.Change goes on in all aspects of language.Grammatical teatures change as do speech sounds,and changes in vocabulary are sometimes very extensive and may occur very rap-idly. Vocabulary is the least stable part of any language.

In the second paragraph the passage tells us that______.
A: some backward race doesn't have a language of its own
B: some race in history didn't possess a language of its own
C: any human race,whether backward or not,has a language
D: some races on earth can communicate without language

It may be pointed out that warfare（战争）as practiced by man has no parallel in nature,This is to say that within the more highly developed animal populations of this earth,there is not now.nor has there been similar destruction within a species（物种）itself.In fact,one has to go to the lowliest forms of animal life,such as certain kinds of ants,to find anything comparable to human warfare.It is a curious fact that mankind appears to give the killing of his own kind a good reason by imaging that it is a"law of nature".There are now a lot of wrong ideas about the laws of nature,of which this is one of the most incorrect and fateful（致命的）.Political beliefs have been based upon it with results that have come near to destroying human civilization.The theory that war is a biological necessity.that it is nature′s method of controlling population and believing in the survival（生存）of the strong and the elimination（灭亡）of the weak,is totally wrong and insupportable.Within the last century.when wars have been common all over the world,the human population of the earth has almost doubled.

The author of this passage seems to be the"law of nature".

A.against
B.in favor of
C.uncertain of
D.very much interested in

共用题干
Lakes,Too,Feel Global Warming

There's no doubt:In the last few decades,the average temperature on Earth has been higher than it has
been in hundreds of years.Around the world,people are starting to measure the effects of global warming一
and trying to figure out what to do about it.
Scientists recently used satellites to study the temperatures of lakes around the world,and they found
that lakes are heating up.Between 1985 and 2009,satellites recorded the nighttime temperatures of the sur-
faces of 167 lakes.During those 24 years,the lakes got warmer by an average of about 0.045 degree
Celsius per year.
In some places,lakes have been warming by as much as 0.10 degree Celsius per year. At that rate,a
lake may warm by a full degree Celsius in just 10 years.That difference may seem small一you might not
even notice it in your bath.But in a lake,slightly warmer temperatures could mean more algae（水藻）,and
algae can make the lake poisonous to fish.
The study shows that in some regions,lakes are warming faster than the air around them.This is impor-
tant because scientists often use measurements of air temperature to study how Earth is warming. By using
lake temperatures as well,scientists can get a better picture of global warming. The scientists say data on
lakes give scientists a new way to measure the impact of climate change around the world.
That's going to be useful,since no country is too big or too small to ignore climate change.Scientists
aren't the only ones concerned.Everyone who lives on Earth is going to be affected by the rapid warming of
the planet. Many world leaders believe we might be able to do something about it,especially by reducing the
amount of greenhouse（温室）gases we put into the air.
That's why the United Nations started the Framework Convention on Climate Change,or UNFCCC.
Every year the convention meets,and representatives from countries around the world gather to talk about
climate change and discuss global solutions to the challenges of a warming world.

Scientists have been keeping records of lake temperatures for over 30 years.
A:Right
B:Wrong
C:Not mentioned

If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet.By the middle of the 21st century,if present trends continue, we will have used up all the oil that drives our cars,for example.Even if scientists develop new ways of feeding the human race,the crowded conditions on earth will make it necessary for lus to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however,has recently been suggested by American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are compleetely exhausted it will be possible to change the atmophere of Venus and so create a new world almost as large as earth itself. The difficult is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms that can live in extremely hot or cold atmospheres and at the same time produce oxygen,should be bred in condition similar to those on Venus.As soon as this has been done, the algae will be placed in small rockets. Spaceship will then fly to Venus and fire the rockets into the atmosphere .In a fairly short time, the alge will break down the carbon dioxide into oxygen and carbon.
When the algae have done theri work, the atmosphere will become cooler,but befor man can set foot on Venus it will be neccessary for the oxygen to produce rain. The surface of the planet will still be too hot for man to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.
Algae are plants that can____.

a.live in very hot temperatures
b.live in very cold temperatures
c.manufacture oxygen
d.all of the above

共用题干
第二篇
Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO₂).Car emissions are a major problem, but the truth is that more CO₂ comes from the energy used at home.The average household creates around
five and a half tonnes of CO₂ a year,and it is the same CO₂ that is changing the climate and damaging the environment.
CO₂ and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO₂ and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.
In 2008,the total UK CO₂ emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO₂ emissions.These figures show that a significant amount of CO₂ results from ordinary citizens carbon footprint in their daily activities and lifestyle.
The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．

What is the author's opinion about the level of CO₂ emissions in the UK?
A:The majority of CO₂ emissions come from motorized transport.
B:CO₂ emissions may cause climate change in the future.
C:More CO₂ emissions come from homes than from cars.
D:The average citizen does not create much CO₂.

共用题干
第二篇

Human and the Earth

In terms of the evolution of life on Earth,human beings have just arrived.Despite their shori time on Earth,however,people have brought about enormous changes to the surface of the planet一changes far out of proportion to the interval of time they have occupied it.
People have more control over their surroundings than any other species on Earth.With the combination of intelligence and manual skill(allowing us to make and use tools),people have found ways to use plant and animal resources,mineral ores,fuels,and many other materials and resources from the Earth.
As the number of people on Earth increases,it becomes increasingly difficult for the population to survive on the resources of the land.The amount of land is limited.Although agricultural production can be increased by use of machinery such as tractors and the addition of fertilizer,the land ultimately can produce only so much food and no more.
As the human population grows,people consume more.Clearly,some locations on Earth already have too many people;in many of these areas,future increases will surely bring about more poverty and suffering. Yet people in rich nations use proportionally far more of the available resources than people in poorer nations.As they consume these resources without restraint,they also waste large amounts of them.
People are only a very small fraction of all the living things on the planet.Yet their numbers create a drain on resources that can't be renewed.For example,the amount of water on Earth is limited,this water is cleaned through natural processes.However,the natural processes for filtering water can clean only a certain amount of water by removing the pollution.Likewise,a limited amount of petroleum can be found under the Earth's surface.Petroleum is a valuable resource.Should people use it up to manufacture petrol for automobiles?As people work to control the planet and make life comfortable,are they using up resources that are needed for their survival?

in terms of the evolution of life on Earth,the history of human beings is_______.
A:very short
B:very long
C:as long as that of other animals
D:as long as that of the Earth

共用题干
第二篇
Around 45%of the UK's carbon dioxide emissions come from the energy people use every day-at home and when they travel.In order to generate that energy,fossil fuels(coal oil,and gas)are burnt,and these produce greenhouse gases-in particular carbon dioxide(CO₂).Car emissions are a major problem, but the truth is that more CO₂ comes from the energy used at home.The average household creates around
five and a half tonnes of CO₂ a year,and it is the same CO₂ that is changing the climate and damaging the environment.
CO₂ and various other gases wrap the earth in an invisible blanket helping to prevent heat from escaping.Without this greenhouse effect,the average temperature on Earth would be around-18℃， compared with the current average of around+15℃．The composition of this blanket of gases has remained relatively constant for many thousands of years.However,since the industrial revolution began around 200 years ago,people have been burning increasing amounts of fossil fuels,thus releasing more CO₂ and other greenhouse gases in the process.This has increased the heating effect of the blanket,trapping more of the sun's energy inside the Earth's atmosphere in turn the Earth's temperature has increased more rapidly in a shorter period of time than it has for thousands of years.
In 2008,the total UK CO₂ emissions were 533 million tonnes.27%(144 million tonnes)of those emissions came from the energy used to heat,light,and power homes.Transport emissions caused by passenger cars,buses and motorcycles accounted for a further 16%(87 million tonnes)of the UK's CO₂ emissions.These figures show that a significant amount of CO₂ results from ordinary citizens carbon footprint in their daily activities and lifestyle.
The effects of climate change can be seen all around us.Weather patterns are becoming more and more fractured and uncertain,and over the last century trends in warm weather have become increasingly common.In the UK in the last 40 years,winters have grown warmer,with much heavier rainfall.One of the clearest shifts over the last 200 years is towards summers that are hotter and drier,causing pervasive（普遍的）water shortages.Recent years have been the hottest since records began and during August 2003,the hottest ever outdoor temperature in the UK was recorded-38.5℃．

What is the author's main aim?
A:To explain the greenhouse effect.
B:To describe the effects of climate change in the UK.
C:To show how much CO₂ is produced by ordinary people's activities.
D:To illustrate how industrial activity creates the greenhouse effect.

共用题干
Some Things We Know About Language
Many things about language are a mystery,and many will always remain so.But some things we do know.
First,we know that all human beings have a language of some sort. There is no race of men anywhere on earth so backward that it has no language,no set of speech sounds by which the people communicate with one another. Furthermore,in historical times,there has never been a race of men without a language.
Second,there is no such thing as a primitive language.There are many people whose cultures are undeveloped,who are,as we say,uncivilized,but the languages they speak are not primitive .In all known languages we can see complexities that must have been tens of thousands of years in developing.
This has not always been well understood;indeed,the direct contrary has often been stated.
Popular ideas of the language of the American Indians will illustrate.Many people have supposed that the Indians communicated in a very primitive system of noises.Study has proved this to be nonsense .There are,or were,hundreds of American Indian languages,and all of them turn out to be very complicated and very old.They are certainly different from the languages that most of us are familiar with,but they are no more primitive than English and Greek.
A third thing we know about language is that all languages are perfectly adequate. That is, each one is a perfect means of expressing the culture of the people who speak the language.
Finally,we know that language changes.It is natural and normal for language to change;the only languages which do not change are the dead ones.This is easy to understand if we look backward in time.Change goes on in all aspects of language.Grammatical teatures change as do speech sounds,and changes in vocabulary are sometimes very extensive and may occur very rap-idly. Vocabulary is the least stable part of any language.

According to the author,language changes are most likely to occur in______.
A: grammar
B: pronunciation
C: vocabulary
D: intonation

共用题干
Some Things We Know About Language
Many things about language are a mystery,and many will always remain so.But some things we do know.
First,we know that all human beings have a language of some sort. There is no race of men anywhere on earth so backward that it has no language,no set of speech sounds by which the people communicate with one another. Furthermore,in historical times,there has never been a race of men without a language.
Second,there is no such thing as a primitive language.There are many people whose cultures are undeveloped,who are,as we say,uncivilized,but the languages they speak are not primitive .In all known languages we can see complexities that must have been tens of thousands of years in developing.
This has not always been well understood;indeed,the direct contrary has often been stated.
Popular ideas of the language of the American Indians will illustrate.Many people have supposed that the Indians communicated in a very primitive system of noises.Study has proved this to be nonsense .There are,or were,hundreds of American Indian languages,and all of them turn out to be very complicated and very old.They are certainly different from the languages that most of us are familiar with,but they are no more primitive than English and Greek.
A third thing we know about language is that all languages are perfectly adequate. That is, each one is a perfect means of expressing the culture of the people who speak the language.
Finally,we know that language changes.It is natural and normal for language to change;the only languages which do not change are the dead ones.This is easy to understand if we look backward in time.Change goes on in all aspects of language.Grammatical teatures change as do speech sounds,and changes in vocabulary are sometimes very extensive and may occur very rap-idly. Vocabulary is the least stable part of any language.

According to the author,people of undeveloped cultures can have______languages.
A: complicated
B: uncivilized
C: primitive
D: well-known