if引导宾语从句的用法

① 在一般将来时中，if 通常解释为“如果”。

例如：I will go shopping if it's sunny tomorrow.

② if 也可以解释为“是否”，与 whether 同义。

例如：I don't know if he is at home now.

1、主将从现：

If it rains（从句）,I will stay at home（主句）.

=I will stay at home if it rains.

2、一般现在时：

If you drive too fast,you may have an accident.

=You may have an accident if you drive too fast.

3、主句为祈使句，从句要用一般现在时态：

Don't play computer games if you don't finish your homework.

whether 和 if 都可以引导宾语从句，表示“是否”，在口语或间接引语中两者可以互换使用。例如：

I wonder if/whether I can get some advice from you.

Ask him whether/if he can come.