It was very kind of you to clean the office,though youA.needn't do B.wouldn't haveC.didn't have to D.mustn't have done为什么选C

问题描述:

It was very kind of you to clean the office,though you
A.needn't do B.wouldn't have
C.didn't have to D.mustn't have done
为什么选C

C..
你打扫教室真是太好了,虽然你不需要这么做..
have to...不得不..
前面用was,过去时,所以后面用过去时..