He must have lost the key the day before yesterday,_____?

问题描述:

He must have lost the key the day before yesterday,_____?
A.must he B.hasn't he C.needn't he D.didn't he
答案应该选D,为什么不选B?请说明原因,

must + have done 时表示推测的一种句型,表示对过去发生动作的推测时,看作一般过去时态,也就是看作lost即可,后面问句就应该用一般过去时态(所以这里选了didn't he).