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could (不能用 can) have done 表示“过去本能够做某事却未做.”注意：其否定形式 couldn't have done 没有虚拟语气的用法,couldn't have done 只能表推测,相当于 can't have done,意为：“过去不可能做了某事.” mustn't have done和can't have done的区别最好有例子 最佳答案 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 thrown B.must;must have thrown. C.must;needn't D.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. 三、“may / might + have + 过去分词”表示对已发生的动作或存在的状态进行不肯定的推测,might的语气比may弱一点.这种结构主要用于肯定句和否定句,疑问句改用can或could.如： They may not have known it beforehand. You might have read about it in the papers. 四、“need + have + 过去分词”表示过去做了不必做或不需要做的事情,或过去做某事纯属多余.如： Need they have done it last week? I needn't have bought so much wine—only five people came. 五、“should / ought to + have + 过去分词”表示过去本该做某事但没做,其否定式表示过去不该做某事但做了,这种句式含有不满或责备之意,ought to的语气比should强一些.如： You ought to / should have studied harder.你本应该更努力学习的.（但没有） He oughtn't to / shouldn't have done that.他本来就不该做那件事.（可是做了） 六、“would ＋ have ＋ 过去分词”表示对过去的某种情况进行猜测,或本来要做某事却因某种原因未做成,通常用来说明某一情况,但不像用should或ought to那样含有责备之意.如： I guess the poet would have been about twenty when she wrote her first poem. Another worker wouldn't have acted like that 请问老师，wouldn't have done 都有哪些用法？ 它和would have done 用法是否完全相同？ 【答】从网友的提问看出，似乎是：否定的wouldn't have done，能否表示对过去情况的推测？ 答案应该是肯定的。例如： Any thinking person would not have accepted such a condition. 任何一个有思想的人（在当时）是都不会接受这个条件的。 A wiser man would not have done such a foolish thing. 聪明一点的人是不会干出这等蠢事的。 【说明】上句话有两层意思： 1. 对过去情况的推测。 2. 隐含的虚拟语气。等于：If he had been a wiser man, he would not have done such a foolish thing. |
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