单选题Starting with the _____ that there is life on the planet Mars, the scientist went on to develop his argument.A premiseB pretextC foundationD presentation

Stephen Hawking believes that earth is unlikely to be the only planet ______ life has developed gradually.

For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain, Lewis and Clark journeyed into the American wilderness to find out what the U.S. had acquired when it purchased Louisiana, and the Apollo astronauts rocketed to the moon in a dramatic show of technological muscle during the cold war.
　　Although their missions blended commercial and political-military imperatives, the explorers involved all accomplished some significant science by going where no scientists had gone before.
　　Today Mars looms as humanity’s next great terra incognita. And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet’s reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role? The question naturally invites a couple of others; Are there experiment that only human could do on Mars? Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary space?
　　With Mars the scientific stakes are arguably higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteorite from Mars. A more conclusive answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science: the prevalence of life in the universe.

Reduced voltage applied to a motor during the starting period will （）.

Starting with the _____ that there is life on the planet Mars, the scientist went on to develop his argument.

The greatest chance for the existence of extraterrestrial life is on a planet beyond our solar system. The Milky Way galaxy alone contains 100 billion other suns, many of which could be accompanied by planets similar enough to Earth to make them suitable abodes of life.　 The statement above assumes which of the following?

Directions: In this section, there is one passage followed by 5 questions. Read the passage carefully, then answer the questions in as few words as possible (not more than 10 words). Remember to write the answers on the Answer Sheet.　　Questions 1-5 are based on the following passage.　　If you were on a distant planet, and if you had instruments that could tell you the composition of Earth’s atmosphere, how would you know there was life on this planet?Water in the atmosphere would suggest there could be water on the surface, and as we all know water is considered crucial to life. But water would only suggest that life is possible. It wouldn’t prove it’s there.　　Carbon? That basic component of “life as we know it?” Not necessarily. A diamond is pure carbon, and it may be pretty, but it isn’t alive.　　What really sets Earth apart is nitrogen, which makes up 80 percent of the planet’s atmosphere. And it’s there only because there is abundant life on Earth, say scientists at the University of Southern California　　The report grew out of a class discussion two years ago in a course taught by Capone and Kenneth Nealson, professor of earth sciences. Students were asked to come up with different ideas about searching for life on other planets. What is a distinct “signature,” as Capone puts it, that would show there is life on another planet?　　That’s a question that has been kicked around in many quarters in recent decades, especially since all efforts to find some form of life, no matter whether on Mars or in the distant reaches of space, have failed. At least so far.　　The current effort to search for some evidence of life on Mars focuses primarily on the search for water, because it has long been believed that water, or at least some fluid, is necessary for the chemical processes that lead life to take place. But that’s probably the wrong approach, the USC group argues.　　“It’s hard to imagine life without water, but it’s easy to imagine water without life,” says Nealson, who was on the Mars team before moving to USC.　　But nitrogen would be a much clearer signature of life. Only about 2 percent to 3 percent of the Martian atmosphere is nitrogen. That’s just a trace, and it probably means there is no life on Mars today, and if there was in the past, it probably ended many, many years ago.　　But, the USC team adds quickly, that doesn’t mean there’s no life anywhere else in the universe. They don’t know where, of course, but they may have found a way to narrow down the search. Look first for nitrogen, then look for biological activity that should be there.　　So if life exists elsewhere, and is similar to life as we know it, there should be nitrogen, and that’s what we should be looking for first, the researchers say.　　If they don’t find nitrogen on Mars, Capone says, “that will probably bring us to the conclusion that there likely never was life on Mars.”　　But how about elsewhere? Could this technique be used to search for life in other solar systems?　　Maybe. It might be possible to detect a nitrogen-rich atmosphere around a planet orbiting another star, but not yet. Current instruments aren’t that sensitive.　　If they ever are, the search for life might be narrowed down to the most promising prospects, chiefly because of the presence of nitrogen. And won’t that be fun!　　Questions:　　1．What can suggest life is possible but cannot be proved according to the author?　　2．What is a clear “signature” of life on another planet according to Capone?　　3．What is considered as a wrong way to search for evidence of life on Mars?　　4．What can probably prove there is no life on Mars today based on the new theory?　　5．Why is it impossible to use the new technique to search for life in other solar systems now?

In an operating diesel engine, which of the following condition is an indication of a leaking air starting valve?（）