引導的三種從句

　　一是條件狀語從句，譯為“如果”。

　　He will come if you invite him. 如果你請他，他會來的。

　　二是賓語從句，譯為“是否”。

　　I wonder if she is ill. 不知她是否病了。

　　三是引導非真實條件句，使用虛擬語氣，譯為“假如,要是”。

　　If I were you, I would never do that.

　　如果我是你，我決不做那件事。

　　拓展

　　一、由when , as soon as , not until 等引導的時間狀語從句也是遵循“主將從現”原則。

　　如：I will tell him about it as soon as he comes back.

　　他一回來我就告訴他這件事。

　　二、if 也可引導賓語從句，意思是”是否“

　　如： I don't know if he will come tomorrow.

　　我不知道他明天是否回來。