阅读理解。 When we can see well, we do not think about our eyes often. It is only when we can not see perfectly that we come to see how important our eyes are. People who are nearsighted can only see things that are very close to their eyes. Many people who do a lot of close work, such as writing and reading, become nearsighted. Then they have to wear glasses in order to see distant things clearly. People who are farsighted face just the opposite problem. They can see things that are far away, but they have difficulty reading a book unless they hold it at arm's length. If they want to do much reading, they must get glasses too. Other people do not see clearly because their eyes are not exactly the right shape. This, too, can be corrected by glasses. Some people's eyes become cloudy because of cataracts. Long ago these people often became blind. Now, however, it is possible to operate on the cataracts and remove them. When night falls, colors become fainter to the eyes and finally disappear. After your eyes have grown used to the dark, you can see better if you use the side of your eyes rather than the centers. Sometimes, after dark, you see a small thing to one side of you, which seems to disappear if you turn your head in its direction. This is because when you turn your head, you are looking at the thing too directly. Men on guard duty sometimes think they see something moving to one side of them. When they turn to look straight at it, they can not see it any more, and they believe they were mistaken. However, this mistake happens because the center of the eye, which is very sensitive in daylight, is not as sensitive as the sides of the eye after dark. 1. We don't know that our eyes are of great importance until _____. [     ] A. we think about our eyes B. we cannot see clearly C. we wear glasses D. we have to do much reading 2. According to the passage, a _____ is more likely to be nearsighted. [     ] A. student B. doctor C. guard D. painter 3. People who are farsighted _____. [     ] A. can do a lot of close work without glasses B. can only see things that are very close to their eyes C. have difficulty reading a book if they hold it at arm's length D. can correct their eyes by glasses 4. To see a small thing at night, it is better to look _____. [     ] A. with wide open eyes B. with half shut or narrowed eyes C. straight at it D. in a slightly different direction