can't have done（不可能做过）是must have done（一定做过）的否定形式.couldn't have done(可能没做过)是may have done(有可能做过)的否定形式.一般认为can't have done有80%以上的把握.而couldn't have done则委...
情态动词can't have done 和couldn't have done 有什么区别吗
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