新东方考研语法讲堂62
4、can/could have done：用来谈过去的情况（1）在疑问句、否定句中，表示怀疑和不可能，这时它们没有时间上的差别，只是could的语气更弱一些：
Who could have taken them? 谁会把它们拿走了呢？
Where can he have gone? 他可能到哪儿去了呢？
He can’t have taken it home. 他不可能是带回家去了。
She couldn’t have left so soon. 她不可能这么快就走了。
I don’t see how I could have done otherwise. 我看不出我当时还有别的做法。
Who could have supposed you were going to do such a thing? 谁会想到你会做出这样的事情。
Nobody could have foreseen such a calamity. 这样的灾祸谁也不会预想到。
（2）could have done(但不是can)在肯定句中，表示“那时本来可以…；差点就要…”，有时用来进行婉转地批评（与might同意，但语气更强一些）：
We could have solved the problem in a more reasonable fashion. 这个问题我们本来是可以更合理得解决的。
He could have told her, but he did not choose to. 他本来可以告诉她的，但他不愿这样做。
When she heard the news, she could have cried. 听了这消息，她简直要哭出来了。
I could have died laughing. 我简直要笑死了。
You could have been more considerate. 你其实可以想的更周到一些。
We could have started a little earlier. 我们其实可以更早一些动身的。
The result could have been better. 结果本可以更好一些。
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