couldn't have done的用法

couldnt have done是情态动词加现在完成时，表对过去的推测，意思是“本不能做某事，实际上做了”。

例句

You couldnt have chosen any gift better for me!

你再也挑不到比这更好的礼物送我了！

You couldn\'t have left it on the bus, could you?

你不可能把它落在公共汽车上了吧？

It couldn\'t have been me ─ it must have been someone else.

那不可能是我——准是别人。

The damage couldn\'t have been caused accidentally.

这次损毁不可能是偶然因素造成的。