SAT语法：时间状语从句时态

一.主从句时态呼应，即主句用现在时，从句也用现在时;主句用过去时，从句也用过去的某种时态，除此之外，主句用将来时，从句依然要用现在时。

eg. Be careful when you cross the road。

When he was seven years old, he could swim.

When she leaves, she will turn off the light.

二. 不同的时间状语需要搭配不同时态的使用：

1.Often,usually———-动词原型do,does,am,is, are

2.yesterday,last Sunday,in the past——-动词过去式did,was,were

3.now——–be+doing

4.while,at that time,——-was doing,were doing

5.since从句,for 2 days,——have done,have been

since+过去的某个时间点—-had done,had been

一般现在时：every…, sometimes, at …, on Sunday,

一般过去时：yesterday, last week, an hour ago, the other day, in 1982, just now

一般将来时：next…, tomorrow, in+时间,

现在完成时：for, since, so far, ever, never, just, yet, till/until, up to now, in past years, always, recently

过去完成时：before, by, until, when, after, once, as soon as

过去进行时：this morning, the whole morning, all day, yesterday, from nine to ten last evening… when, while

将来进行时：soon, tomorrow, this evening, on Sunday, by this time, tomorrow, in two days, tomorrow evening