if引導的從句3種情況:

1.條件狀語從句，譯為“如果”。

結構：if+一般現在時，主語+將來時

If you ask him, he will help you.

He will come if you invite him.

2.賓語從句，譯為“是否”。

I wonder if she is ill.

不知她是否病了。

I want to know if he lives there.

我想知道他是否住在那兒。

He asked me if I could help him. 他問我是否能幫他。

3.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.