twice a year, whether it is a car or a bus or a truck, is the rule that every driver must obey in this city.

A．Examining

B．Examined

C．Being examined

D．Having been examined

以下为产生双眼单视的必要条件，除外（）

A.双眼能共同注视目标

B.有良好的网膜及视神经传导功能

C.视皮质具有融像功能

D.双眼无恒定性斜视

E.双眼屈光状态必须正常