求宾语从句的有关知识,

以下四种情况只能用whether.
1)句子后面出现了or not,只能用whether.
eg.I don't know whether he still works in that factory or not.
2)在谓语动词中出现了介词.
eg.I wonder about whether he is ok.
3)后接动词不定式时,只能用whether.
eg.I haven't decided whether to go there with him.
4)引导主语从句时,只能用whether.
Whether he'll go there is still unknown.