问题补充：
-- Who do you think such a foolish thing?
-- It Tom, but I’m not sure.
A. could have done; may have been
B. could have done; must have been
C. should have done; may be
D. must have done; might have been
答案：
(答案→)A. could have done; may have been
B. could have done; must have been
C. should have done; may be
D. must have done; might have been
解析：考查情态动词的完成式的用法：句意：--你认为谁会做这么愚蠢的事情？--可能是汤姆，我不确定。第一空填could have done，could表示推测的时候，用于疑问句和否定句中，第二空填might have done表示不确定的推测，因为后面说but I’m not sure。should have done本应该做而没有做，must have done过去一定做了，选A。
