英语之中宾语从句的连词that if weather用发上有什麽区别啊?

1.陈述句用that连接
比如：He said that he was a middle school studen.
that可以省略
2.if和weather解释为“是否”,改变为宾语从句时,要用陈诉句语序
比如：I want to know if (whether) he lives there
一般情况下,if和weather可以互换,但是如果句子中有or not,必须用weather.weather...or not是固定搭配!