I don't know the reason why he did't come to the meeting yesterday morning.为什么不可以用that引导那这句怎么解释The reason that (why)he missed the train is that he got up late.

问题描述:

I don't know the reason why he did't come to the meeting yesterday morning.为什么不可以用that引导
那这句怎么解释The reason that (why)he missed the train is that he got up late.

表示原因的,当然要用WHY

the reason why .... 记好这结构,,

the reason 表原因理由做先行词时只能用why 来引导
那就补充一下吧
楼主后给出的哪个句子中的是定语从句,用that ,因为此时不表示理由了,只有在表示理由的时候才可以用why

这是固定搭配啦,reason后面的从句必须用why来引导,表示因果关系