问题补充:
He have finished his work; Otherwise, he would.not be enjoying himself by the seaside.
A. should
B. must
C. couldn’t
D. can’t
答案:
A. should
(答案→)B. must
C. couldn’t
D. can’t
解析:考查情态动词表推测的用法。must have done 表示对过去事情肯定的推测,用于肯定句中,句意:他一定完成工作了,否则的话他就不会再海边玩的这么高兴了。所以选B。