无论是面对UKiset考试的哪个科目，UKiset语法都是我们必备的基础能力，在Ukiset语法学习我们常常会走入一些盲区，为了帮助大家更好的备考UKiset语法，下面就跟着小编一起来学习一下吧！
1) could have + 过去分词
A. 表示对过去可能发生的事情的推测，意为，“可能做了某事”。
He couldn’t have seen her yesterday.
They could have lost their way.
B. 表示某事在过去本有可能发生，但事实上并未发生，意为，“本可以做某事”。
We could have started a little earlier.
I could have killed her. It was a narrow escape.
2) may (might) have + 过去分词
A. 表示对过去情况的推测，意为，“可能已做某事”。
He may have heard the news.
I might have come to a wrong conclusion.
B. 表示一种未实现的可能性，即本可以做某事，而实际上并没有做，有时含有抱怨的口吻。
It was a narrow escape. You might have killed yourself.
A lot of men died who might have been saved.
3) must have + 过去分词
表示逻辑上的必然性，即按照某些现象推断过去肯定发生过的某事。
She must have made a big mistake.
The city at one time must have been prosperous, for it enjoyed a high level of civilization.
4) needn’t have + 过去分词
表示过去不必做某事，但已经做了，即本可不必做某事。
You needn’t have woken me up. I don’t have to go to work today.
He needn’t have watered the flowers, for it is going to rain.
5) should / ought to have + 过去分词
表示过去应该做某事而实际上没有做。
You should / ought to have done what your parents told you. (But you failed to do it.)
You should / ought to have been more careful. (But you weren’t.)
6) shouldn’t / oughtn’t to have + 过去分词
表示过去不应该做某事而实际上却做了。
You shouldn’t / oughtn’t to have crossed the road when the lights were red. (But you did.)
They shouldn’t / oughtn’t to have left so soon. (But they did.)
7) would have + 过去分词
表示对现在或将来某时之前业已完成的动作的推测。可译为，“可能”、“也许”、“想必”。
He would have arrived by now.
She would have recovered by then.
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