It really seemed ages _____ the police came on the scene and cleared away the damaged

　　　　cars.

A．before

B．after

C．when

D．as

通信电源都具备以下（）保护功能。

A.输入过、欠压保护 

B.输出过压保护 

C.输出短路保护 

D.过温保护 

E.电池欠压保护