if (假设，如果)，unless (除非)，so/as long as (只要)，suppose/supposing (that)(倘若，假设); only if (只有......才)，provided/providing (that)(如果)，on condition that (条件是)，in case (如果，万一)，when (如果；既然，考虑到)。

　　If Tom passes the examination，his father is going to buy him a bicycle.

　　如果汤姆考试及格，他父亲将会给他买一辆自行车。

　　You may watch TV as long as you finish your homework.只要你做完作业，你就可以看电视。

　　Suppose/Supposing the plane does not arrive on time，what shall I do?

　　假定飞机不能准时到，我该怎么办？

　　How can they learn anything when they spend all their spare time watching television？既然他们把所有空闲的时间都用来看电视了，还能学到什么东西呢？

　　Only if you take an active part in physical activity will you be able to keep fit and stay healthy.

　　只有积极参加体育锻炼，你才能保持身体健康。

　　2．主将从现

　　条件状语从句如果主句表示将来的时间，从句用一般现在时代替一般将来时。

　　I won't wait for him unless he calls me.

　　除非他给我打电话，否则我不会等他。

　　[即时训练1]　单句语法填空

　　①It is so cold that you can't go outside unless fully covered in thick clothes.

　　②I believe you will have a wonderful time here once you get to know everyone else.

　　③I told him he would succeed only if he tried hard.

　　二、让步状语从句

　　让步状语从句常由以下从属连词引导：

　　though/although (尽管，虽然)，as，even if/even though (即使)，疑问词­ever/no matter＋疑问词(不管，无论)等。

　　1．though，although; even if，even though"虽然，尽管"。

though，although这两者意思大致相同，一般可互换，都可与yet，still，nevertheless连用，但不能与but连用。