He have completed his work；otherwise he wouldn’t be enjoying himself by the seaside.A. s

问题补充：

He have completed his work；otherwise, he wouldn’t be enjoying himself by the seaside.

A. should

B. must

C. wouldn’t

D. can’t

答案：

A. should

(答案→)B. must

C. wouldn’t

D. can’t

解析：考查情态动词用法。Should have done本应该做某事，实际上却未做；must have done一定做了某事；can’t have done不可能做了某事；句意：他一定完成了作业，要不然，他不会在海玩得那么开心。根据后半句话说明他在海边玩得很开心，那么他已经完成了作业，这是一个过去发生的事情，使用“情态动词+have done”对过去发生的事情进行推测。故B正确。