—You shouldn’t have shouted at your mother. It really hurt her—Exactly. I crazy at the

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A. must be
B. could be
(答案→)C. must have been
D. could have been
解析：句意：--你不应该对你妈妈大声说话的。这真的伤害了她。--确实是，我那时一定是发疯了。从shouldn’t have done说明是过去的事情，所以排除AB，must have done是对过去情况的肯定推测，could have done是“过去本可能做却没做“，不符合句意。选C。