不一定by the time 有两个意思1.到...为止,一般要求主句用过去完成时.He had left by the time we reached home.当我们到家的时候他已经走了.The movie had begun by the time we got there.当我们到那儿的时候,电影...By the time we arrived the meeting was over. 为什么不用完成时？会议结束这个动作不是已经完成了吗？be over是一个状态了，不是动作