职称英语理工类的A级阅读理解练习(4)

　　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 still our workhorse. 　　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 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. 　　1. Most computer users want to know how the computer mouse works. 　　2. According to the author, general computer users need not know how the computer mouse was invented. 　　3. The computer mouse derives its name from the cable that goes out its body, which looks like the tail of a mouse. 　　4. The key components of a computer mouse are the two LEDs. 　　5. When an ordinary computer mouse gets dirty, it has to be replaced with a new one. 　　6. The most durable computer mice on sale are the IBM ones. 　　7. The optical mouse is superior to the basic one in that the former has no moving parts.