其否定式为:cannot have done。 You must have seen the film.
You cannot have seen the film.
needn’t+ have done:本来不必要做的而实际上又做了。 You needn’t have watered the flowers,for it is going to rain.
注意:didn’t need to(have to)do:
没有必要做而实际上也没有做
I didn’t need to clean the windows.My sister did it 2 hours ago.
should(ought to)+ have done:本来应该做而实际上又没有做。其否定形式表示某中行为不该发生却发生了。 You should have started earlier, but you didn’t.
She shouldn’t have taken away my measuring tape,
for I worked to use it.
注意:He should have finished the work by now.(表推测)
虚拟语气
类
别 用
法 例
句
If引导的
条件从句 与现在事实相反 从句动词:过去式(be用were)
主句动词:should/would/could/might+do If he were here, he would help us.
与过去事实相反 从句动词:had+done
主句动词:should/would/could/might+have+done If I had been free,I would have visited you.
与将来事实相反 从句动词:过去式/should+动词原形/were+to do
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