一、条件状语从句用法

1. 引导条件状语从句最常用的连词是if,由if引导的条件状语从句表示在某种条件下某事很可能发生。如:

If you ask him, he will help you.如果你请他帮忙,他会帮你的。

If you fail in the exam, you will let him down.如果你考试不及格,你会让他失望的。

另外，if从 句还表示不可实现的条件或根本不可能存在的条件,也就是一种虚拟的条件或假设,从句多用一般过去时或过去完成时。如:

If I were you, I would invite him to the party.如果我是你,我会邀 请他参加聚会。

2. unless = if...not.　 除非,若不,除非在……的时候

例如：Let's go out for a walk unless you are too tired.

=If you are not too tired, let's go out for a walk.

Unless it rains, the game will be played.除非下雨,比赛将照常进行。

3. so/as long as只要

例：You may borrow my book as long as you keep it clean. 　　只要你保持书的清 洁，你就可以把我的书借去。

So long as you're happy, it doe sn't matter what you do. 只要你高兴，你做什么都没有关系。