英语 › 必修第三册 › 必三 U5 › 情态动词
过去推测：must have done 一定做了，can't have done 不可能做了，may have done 可能做了；should have done 本该做却没做。
He must have left already.（他一定已经走了。）
关键词：情态动词 + have done、must have done、should have done、can't have done、对过去的推测