控制当访问者将鼠标指针移动到指定的图片时，下列哪个显示指定层上图片的行为（）A、on Mouse OverB、on Mouse OutC、on Mouse UprD、on Mouse Down

共用题干
Computer Mouse

The basic computer mouse is an amazingly clever invention with a relatively simple design that allows us to point at things on the computer and it is very productive.Think of all the things you can do with a mouse like selecting text for copying and pasting,drawing,and even scrolling on the page with the newer mice with the wheel. Most of us use the computer mouse daily without stopping to think how it works until it gets dirty and we have to learn how to clean it. We learn to point at thing before we learn to speak,so the mouse is a very natural pointing device.Other computer pointing devices include light pens,graphics tablets and touch screen,but the mouse is still our workhorse.
The computer mouse was invented in 1964 by Douglas Englehart of Stanford University.As computer screens became popular and arrow keys were used to more around a body of text,it became clear that a pointing device that allowed easier motion through the text and even selection of text would be very useful.The introduction of the mouse,with the Apple Lisa computer in 1983,really started the computer public on the road to relying on the mouse for routine computer tasks.
How does the mouse work?We have to start at the bottom,so think upside down for now. It all starts with mouse ball. As the mouse ball in the bottom of the mouse rolls over the mouse pad,it presses against and turns two shafts.The shafts are connected to wheels with several small holes in them. The wheels have a pair of small electronic light-emitting devices called light emitting diodes (LED)mounted on either side.One LED sends a light beam to the LED on the other side.As the wheels spin and a hole rotates by,the light beam gets through to the LED on the other side.But a moment later the light beam is blocked until the next hole is in place.The LED detects a changing pattern of light,converts the pattern into an electronic signal,and sends the signal to the computer through wires in a cable that goes out the mouse body.This cable is the tail that helps give the mouse its name.The computer interprets the signal to tell it where to position the cursor on the computer screen.
So far we have only discussed the basic computer mouse that most of you probably have or have used.One problem with this design is that the mouse gets dirty as the ball rolls over the surface and picks up the dirt. Eventually you have to clean your mouse. The newer optical mice avoid this problem by having no moving parts.

When an ordinary computer mouse gets dirty,it has to be replaced with a new one.
A:Right
B:Wrong
C:Not mentioned

共用题干
Computer Mouse

The basic computer mouse is an amazingly clever invention with a relatively simple design that allows us to point at things on the computer and it is very productive.Think of all the things you can do with a mouse like selecting text for copying and pasting,drawing,and even scrolling on the page with the newer mice with the wheel. Most of us use the computer mouse daily without stopping to think how it works until it gets dirty and we have to learn how to clean it. We learn to point at thing before we learn to speak,so the mouse is a very natural pointing device.Other computer pointing devices include light pens,graphics tablets and touch screen,but the mouse is still our workhorse.
The computer mouse was invented in 1964 by Douglas Englehart of Stanford University.As computer screens became popular and arrow keys were used to more around a body of text,it became clear that a pointing device that allowed easier motion through the text and even selection of text would be very useful.The introduction of the mouse,with the Apple Lisa computer in 1983,really started the computer public on the road to relying on the mouse for routine computer tasks.
How does the mouse work?We have to start at the bottom,so think upside down for now. It all starts with mouse ball. As the mouse ball in the bottom of the mouse rolls over the mouse pad,it presses against and turns two shafts.The shafts are connected to wheels with several small holes in them. The wheels have a pair of small electronic light-emitting devices called light emitting diodes (LED)mounted on either side.One LED sends a light beam to the LED on the other side.As the wheels spin and a hole rotates by,the light beam gets through to the LED on the other side.But a moment later the light beam is blocked until the next hole is in place.The LED detects a changing pattern of light,converts the pattern into an electronic signal,and sends the signal to the computer through wires in a cable that goes out the mouse body.This cable is the tail that helps give the mouse its name.The computer interprets the signal to tell it where to position the cursor on the computer screen.
So far we have only discussed the basic computer mouse that most of you probably have or have used.One problem with this design is that the mouse gets dirty as the ball rolls over the surface and picks up the dirt. Eventually you have to clean your mouse. The newer optical mice avoid this problem by having no moving parts.

The computer mouse derives its name from the cable that goes out its body,which looks like the tail of a mouse.
A:Right
B:Wrong
C:Not mentioned