资料：When we see well we do not think about our eyes very often. It is only when we cannot see perfectly that we realize how important our eyes are.

资料：When we see well，we do not think about our eyes very often. It is only when we cannot see perfectly that we realize how important our eyes are.
People who are near-sighted can only see things that are very close to their eyes，Everything else seems blurry（=unclear）.Many people who do a lot of work，such as writing，reading and sewing become near-sighted.
People who are far-sighted suffer from just the opposite problem. They can see things that are far away，but they have difficulty in 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. They have what is called astigmatism. 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.
Having two good eyes is important for judging distances. Each eye sees things from a slightly different angle. To prove this to yourself，look at an object out of one eye；Then look at the same object out of your other eye. You will find the object’s relation to the background and other things around it has changed. The difference between these two different eye views helps us to judge how far away an object is. People who have only one eye cannot judge distance as people with two eyes.

We should take good care of our eyes______.

A.even if we can see well
B.only when we cannot see perfectly
C.only when we realize how important our eyes are
D.only when we can see well

答案：A解析：本题考查的是细节理解。
【关键词】take good care of；our eyes
【主题句】第1自然段When we see well，we do not think about our eyes very often. It is only when we cannot see perfectly that we realize how important our eyes are. 当我们看东西很清楚的时候，我们不经常想到我们的眼睛。只有当我们无法完美地看到时，我们才意识到我们的眼睛多么重要。
【解析】本题的问题是“我们应该好好保护我们的眼睛________”A选项“即使我们能看得很清楚”；B选项“当我们无法完美地看到时”；C选项“只有当我们意识到我们的眼睛有多重要时”；D选项“只有在我们能够看得出来的时候”。根据主题句分析可知，我们无论何时都要保护好眼睛，不要在看不清的时候才意识到严重性，故A选项符合题意。