Dentists always ask questions when it is impossible for you to answer

问题描述:

Dentists always ask questions when it is impossible for you to answer
这里的 for you to answer
it is
when
解释下谢谢

when这里跟的是一个时间状语从句,当...时候
it is adj for sb to do sth.这个句型表示对某某人来说做什么事是很.的