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When we can see well, we do not think about our eyes very often. It is only when we cannot 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, reading and sewing, become nearsighted. Then they have to wear glasses in order to see distant things clearly.
People who are farsighted(近视的) suffer from 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(白内障). Long ago these people often became blind. Now, however, it is possible to operate on the cataracts and remove them.
When night falls, colours become fainter to the eye and finally disappear. After your eyes have grown used to the dark, you can see better if you use the sides 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 you 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 cannot see it any more, and they believe they were mistaken. However, this mistake happens because the center of the eye, which is very sensitive(敏感的) in daylight, is not as sensitive as the sides of the eyes 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. tailor B. doctor C. guard D. painter
3. Those who suffer from cataracts _____.
A.will become blind
B.cannot be cured (治愈)
C.may be cured
D.must move to other places
4. People who are farsighted _____.
A.cannot 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.have the same problem as the nearsighted people
5. 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
