1）条件状语从句主要由if, unless, supposing（suppose）引导：

　　if:

　　I must leave if thats the case. 如果情况如此我就得走了。

　　He will come if asked. 如果邀请的话他会来的。

　　unless:

　　I wont write unless he writes first. 我不写信，除非他先给我写。

　　Ill go there tomorrow unless it rains. 除非下雨，否则我明天去那里。

　　supposing:

　　Supposing that he asks you, will you go? 假定他请你去，你会去吗？

　　Supposing his plan goes wrong, what will you do then?

　　
　　suppose:

　　Suppose she finds out, what shall we do then? 假如她发现了，我们怎么办？

　　Suppose you lost your job tomorrow, what would you do? 假定你明天失业，你怎么办？

　　provided:

　　I will agree to go provided（providing） （that） my expenses are paid.

　　如果有人给我掏路费我将同意去。

　　She agreed to go and work there provided that her family could go with her.

　　providing:

　　Ill dry the dishes, providing that you do the washing-up. 如果你刷盘子，我就将它们擦干。

　　2）条件状语从句还有其他形式：

　　You will always have a home as long as I have anything.

　　只要我有家产，你就永远会有一个家。

　　Theyll stand by you even if you dont succeed. 即使你不成功，他们也会支持你。

　　此外，as long as, so long as, in case, even if 都起连词作用。