楼主，您好详细点就是说：1）mustn't have done可意为“本不必”，即已经做了某事，而实际上不必要2)首先have done表示已经做过，这点就不用谈了。can't have done 表示以前不可能做某事。例句---Where____Margaret have put the empty bottles？---She________them away.They must be somewhere.A.can;can't have thrownB.must;must have thrown.C.must;needn'tD.can;must throw答案为A.第一个句子是一个疑问句而且表示可能性的推测，所以只能用情态动词can或could，第二句的答语表示对过去的推测，所以用can't have done. 请看常见的“情态动词 + have + 过去分词”的用法：一、“must + have + 过去分词”表示对过去发生的事情或状态进行推测，语气比较坚定，通常只用于肯定句。如：It must have rained last night, for the ground is wet.You must have been mad to speak to the servant.二、“can / could + have + 过去分词”表示对过去某种情况的怀疑或不确定。can和could一般用于否定句和疑问句，could的语气较can弱。如：I didn't see her at the meeting this morning; she can't / couldn't have spoken at the meeting.He can't have finished the work so soon.
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