How could you have told her为什么是不是had 不是过去式吗?

If I had known that,I could have helped you.had和known怎么都是过去式 8._______ somebody had told us,we could have warned you. if you had told us earlier who he was,we could have introduc If you had told us earlier___he was,we could have introduced i told you it could be done 请问如何翻译,及为什么用could be,could一般不是指能 Have you told her all I told you yesterday? Could you tell me where you went?宾语重句不是时态要保持一致吗,为什么tell没用过去式 情态动词的过去式后面能接完成时吗?比如can he have told a tie和could he have told how long have you had to wait?had 如果是现在完成时,wait为什么不加ed, ”How many times have I told you...!”是个感叹句,为什么没用陈述语序? If I could have told you about cultural differences between You had better have your shoes mended.mended为什么是过去式呢?