Question

I hate _____ when people talk with their mouths full

1. A.
   it
2. B.
   that
3. C.
   these
4. D.
   them

Answer 1

A
考查形式宾语。it是形式宾语，真正的宾语是when people talk with their mouths full，因为hate在此处是及物动词，后面必须加宾语，但是when people talk with their mouths full是一个完整的句子，不能做宾语，就必须用it充当形式宾语。
这个时候when people talk with their mouths full虽然是一个疑问句，但是却是陈述句的形式，when翻译成“当……的时候”。when做“当……的时候”讲的时候，不一定就是引导时间状语从句，它可以用于从句中。比如what：I don't believe what you said.
这里的what同样是疑问词，也作“什么”讲，但是它仅仅是从句的一个成分而已（宾语）。