It last night, for the ground is wet outside.
A. would be raining
B. would have rained
C. must rain
D. must have rained
网友回答
A. would be raining
B. would have rained
C. must rain
(答案→)D. must have rained
解析：考查情态动词表示推测。句意：昨天晚上肯定下雨了，因为外面的地上是湿的。根据句意说明是对过去情态的推测，使用“情态动词+have done”的形式；如果是对现在的情况进行推测，要使用“情态动词+动词原形”的形式。Must have done一定做了某事；would have done本要做某事，实际上却未做（表示虚拟语气）。故D正确。