could+have+done的例句和could not+have+done的例句

could+have+done和could not+have+done是两个概念 1、Could have done = would have done 表虚拟语气i.e:He would not die If I COULD HAVE HELPED him.如果当时我能帮助他,他就不会死.（COULD HAVE HELPED可以和WOULD HAVE HELPED替换,意思一样） 2、Could NOT have done不是虚拟语气Could have done的否定形式.当Could have done变为Could NOT have done时就不再是虚拟语气了,而是表猜测.i.e:He could Not have gone anywhere,I just saw him.他不可能去哪里的,我刚刚都还看见他.）