y 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,电影已经开始了.
2)…当……的时候;
如果只是说过去某个时候的状况,用过去时,而不用完成时.
By the time the war was over ,death and suffering were to be seen everywhere.在战争结束的时候,到处可见死亡和饥饿.这里没有“死亡和饥饿”已经完成的意思,只是描述当时这个时间点的状况.所以用过去时.