三個(gè)詞引導(dǎo)時(shí)間狀語(yǔ)從句時(shí)我區(qū)別.
before ,until 這兩個(gè)詞用一般現(xiàn)在時(shí)表示將來(lái)時(shí).如
I will wait here until he comes back.
It will be two years before he returns.
當(dāng)主句是過(guò)去時(shí)的時(shí)候從句也用過(guò)去時(shí).如
Yesterday I waited until he came back.
He glanced at the watch before he left.
since 有它自己的用法,既它的從句用一般過(guò)去時(shí),主句用現(xiàn)在完成時(shí).
I have worked here since I came here two years ago.