■if 的用法。其意为“如果”:
He抣l do it if you pay him. 如果你付钱,他是会干的。
If you ask him, he will help you. 如果你向他提出请求,他会帮助你。
■unless 的用法。其意为“如果不”、“除非”:
I shall go there tomorrow unless I’m too busy. 如果我不太忙,明天将到那儿去。
Unless you go at once you will be late. 如果你不马上走,就会迟到的。
■as [so] long as 的用法。其意为“如果”、“只要”:
As long as you do your best, we抣l be happy. 只要你尽力,我们就满意了。
You can go out as long as you promise to be back before 8. 如果你保证八点以前回来,你可以出去。