问题
选择题
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
答案
B
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。