第2个回答 2012-02-06
简单举四个例子
I know you are right.
I knew you were right.
I have known you are right.
I had known you were right.
补:讲一个大多数同学忽略的事实,现在完成时属于现在时,过去完成时属于过去时,还是举例子I couldn't remember where I --A----yesteday.A,went B have gone 明白前面所讲现在完成时属于现在时的同学肯定不会问为什么不选B了。