When can people think about our eyes very often? On the time when we______.

When we can see well, we do not think about our eyes very often. It is (16) 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 (17) are very close to their eyes. Many people who do a lot of close work, (18) such as writing, reading and sewing, become nearsighted. They have to wear glasses (19) in order to see distant things clearly. (20) People who are farsighted 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.
Q16: When can people think about our eyes very often?
Q17: What things can nearsighted people see clearly?
Q18: Who will become nearsighted easily?
Q19: Why do nearsighted people wear glasses?
Q20: What problem do farsighted people suffer from?