----- You shouldn’t have talked back to our teacher like that. It was awfully impolite.
----- You are right. I crazy at that moment.
A. could have been
B. can be
C. must have been
D. should have been
网友回答
A. could have been
B. can be
(答案→)C. must have been
D. should have been
解析：对过去事情的猜测用must have done