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