第1个回答 2011-12-20
三个词引导时间状语从句时我区别。
before ,until 这两个词用一般现在时表示将来时。如
I will wait here until he comes back.
It will be two years before he returns.
当主句是过去时的时候从句也用过去时。如
Yesterday I waited until he came back.
He glanced at the watch before he left.
since 有它自己的用法,既它的从句用一般过去时,主句用现在完成时。
I have worked here since I came here two years ago.本回答被提问者采纳
第2个回答 2011-12-23
.时间状语:yet,already,just,never,ever,so far,by now,since+时间点,for+时间段,recently, lately, in the past few years, etc. 现在完成时,基本结构:主语+have/has +p.p(过去分词)+其他
时间状语:since+时间点,for+时间段等.现在完成进行时
时间状语:Before, by the end of last year (term, month…), etc. 过去完成时,基本结构:主语+had + p.p(过去分词)+其他