His work have been completed; otherwise he wouldn’t be enjoying himself on the beach.A.

问题补充：

His work have been completed; otherwise, he wouldn’t be enjoying himself on the beach.

A. should

B. shouldn’t

C. can’t

D. must

答案：

A. should

B. shouldn’t

C. can’t

(答案→)D. must

解析：考察情态动词用法。Should have done本应该做某事，实际上却未做；shouldn’t have done本不应该做某事，实际上却做了。Can’t have done不可能做了某事；must have done一定做了某事；本句的关键在于otherwise后面的句意。句意：他肯定完成了他的工作，要不然，他不会在海滩上玩得那么开心的。根据句意说明这是对过去发生的事情的有把握的肯定推测。故D正确。