He is often heard _______ the English song.

题目

He is often heard _______ the English song.
A.to sing B.sing C.to have sung D.to be singing
2.we don't know _____
A.to do B.to be done C.what to do D.what to be doing
我都知道答案,但是不明白这是什么原理.只句的语感是这样.希望大家能说一下原因.

答案

1.A hear sb do sth变成被动语态后,do sth前面要补上to
2."疑问词+不定式"结构相当于名词,做know的宾语.而"疑问代词+不定式"结构中,进一步要求疑问代词要充当不定式中某个动词或介词的宾语.what充当do的宾语,翻译成"该干什么".