by the time的用法：
1、到…時候為止：
表示到...為止,一般要求主句用過去完成時.
例句：
He had left by the time we reached home.
當(dāng)我們到家的時候他已經(jīng)走了.
The movie had begun by the time we got there.
當(dāng)我們到那兒的時候,電影已經(jīng)開始了.
2、到……的時候：
(1)可以表示將來的時間. 主句用將來完成時,而從句用一般現(xiàn)在時來表示將來的動作.
I will have finished the work by the time my father comes back.
(2)可以表示過去的時間. 主句用過去完成時,而從句用一般過去時.
He had built a lab for himself by the time he was 12 years old.
注：如果只是說過去某個時候的狀況，用過去時，而不用完成時。
例句： By the time the war was over , death and suffering were to be seen everywhere.
在戰(zhàn)爭結(jié)束的時候，到處可見死亡和饑餓。
這里沒有“死亡和饑餓”已經(jīng)完成的意思，只是描述當(dāng)時這個時間點的狀況。所以用過去時。