when ( ) questions in class,one should answear them as clearly as possible.
问题描述：
when ( ) questions in class,one should answear them as clearly as possible.
A asking
B to ask
C to be asked
D asked
选D,为什么不选C
答
when引导的时间状语从句,省略主语和动词,when （one is） asked questions in class,he should answear them as clearly as possible