我想以句子的形式让你明白什么情况下我们只能用whether.下面句子中的whether一般不能被if替换，你自己根据这些句子作以归纳吧，应该没问题。
I wonder whether he will go there or not.
I am considering whether to do the experiment this afternoon.
It depends on whether they have the intention to do it.
They are discussing whether they will go abroad for further study.
Whether the sports meeting will be held just depends on the weather.
The question is whether he will agree to it.
