by the time I came back they had climbed up..by the time I came back they had climbed up ten metres现在完成时的结构不是has/have加动词过去分词么?为什么不用have climbed?

问题描述:

by the time I came back they had climbed up..
by the time I came back they had climbed up ten metres
现在完成时的结构不是has/have加动词过去分词么?为什么不用have climbed?

表示过去的过去,用过去完成时
我返回去是过去的,爬上去十米,是在我返回去前完成的,所以是过去的过去,用过去完成时
had done

这个是过去完成时,表示过期的过去came back表示回去的时候已经是过去了,所以他们向上爬就是“过去的过去”进行的动作,所以用过去完成时

climbed up动作发生在came back 之前
came back 已经是过去时态(by the time到...时候)
过去完成时表示“过去的过去”
实际上,多数用法都有前后动作的时间对比,或暗含对比

came已经是过去式了,climb还要在came之前,故一定是过去完成时