题目内容：

He is not such aperson and he ＿such athing .A:cannot have done B:could not have done 选哪个...
He is not such aperson and he ＿such athing .A:cannot have done B:could not have done 选哪个,为什么?不是虚拟语气嘛!

优质解答

选择B
本句是隐藏了条件句的虚拟语气.
if he were such a person,he could have done such a thing.
如果他是那样的人,他就会做那样的事情了.(这个句子没有问题吧?)
但是“他不是那样的人,所以他不会做那样的事.”这里的条件句不见了,变成了判断句,用一般现在时,说明真实情况.但是后半句还是对过去的推断,所以还是用couldn't have done的形式.
这种情况在英语中很常见.
欢迎探讨.