what you said和what you have said有什么区别例如,i can not understand what you ( ).这里要用哪个?如果前面的can改成could呢?

what you said和what you have said有什么区别例如,i can not understand what you ( ).这里要用哪个?如果前面的can改成could呢?
what you said和what you have said有什么区别
例如,i can not understand what you ( ).这里要用哪个?如果前面的can改成could呢?

what you said和what you have said有什么区别例如,i can not understand what you ( ).这里要用哪个?如果前面的can改成could呢?
就是过去式和现在完成时的区别.
what you said 过去时是过去某一时间里所发生或存在的状态.
what you have said现在完成时跨越两个时间以上,一是过去,一是现在.它的动作发生在过去,但是对现在又影响.
i can not understand what you said.
i could not understand what you have said.