------Tom is never late for work. Why is he absent today?
------ Something to him.
A. must have happened
B. can have happened
C. must happen
D. can happen
网友回答
(答案→)A. must have happened
B. can have happened
C. must happen
D. can happen
解析：根据句意：汤姆从来不迟到。为什么今天迟到了呢？他肯定是出了什么事。
must have done 过去肯定做了某事，对过去的肯定推测。
对过去的否定推测应用 can’t have done.一般没有B这种形式。C表对现在的推测，不对。