by the time的用法：
1、到…時(shí)候?yàn)橹梗?/p>
表示到...為止,一般要求主句用過去完成時(shí).
例句：
He had left by the time we reached home.
當(dāng)我們到家的時(shí)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(shí)候,電影已經(jīng)開始了.
2、到……的時(shí)候：
(1)可以表示將來的時(shí)間. 主句用將來完成時(shí),而從句用一般現(xiàn)在時(shí)來表示將來的動(dòng)作.
I will have finished the work by the time my father comes back.
(2)可以表示過去的時(shí)間. 主句用過去完成時(shí),而從句用一般過去時(shí).
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(gè)時(shí)候的狀況，用過去時(shí)，而不用完成時(shí)。
例句： By the time the war was over , death and suffering were to be seen everywhere.
在戰(zhàn)爭(zhēng)結(jié)束的時(shí)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(shí)這個(gè)時(shí)間點(diǎn)的狀況。所以用過去時(shí)。