单项选择题
A.only when we cannot see perfectly B.only when we can see well C.even if we can see well D.only when we realize how important our eyes are
A.have a curable disease in their eyes B.have eyes that are not exactly the right shape C.have a difficulty that can be corrected by an operation D.have an eye difficulty that cannot be corrected by glasses
A.seeing at night B.seeing objects far away C.looking over a wide area D.judging distances