They must have been enjoying themselves there,otherwise they so long.
A. can’t have stayed
B. wouldn’t have stayed
C. needn’t have stayed
D. couldn’t stay
网友回答
A. can’t have stayed
(答案→)B. wouldn’t have stayed
C. needn’t have stayed
D. couldn’t stay
解析：must have done表示对过去有把握的推测,他们一定在过去那时玩得很高兴。后面是否则他们就不会待这么长时间,这里也是对过去的可能性的推测。