the reason为先行词的定语从句,后面的关系词什么情况用why?什么情况用that等?请举例子说明

从句缺少宾语时用that,缺少原因状语时用why
如：
The reason that he told us is not true.（在从句中做直接宾语）
The reason why he didn't attend the meeting is not clear.（在从句中做原因状语）
我说的明白吗?
此外,The reason 后的从句也可能是同位语从句,判断标准：只保留The reason 和从句（不看主句其他部分）,然后再两者之间加一个is如果语义句法成立,就是同位语从句.换句话说,先行词与同位语从句有逻辑主表关系.
如有问题请追问.

何时用that，琢磨以下句子，其中it 指宾语
That is the reason that he can't say.
That is the reason why he can't say it .
关系副词why，在定语从句中作状语表示原因，why的先行词只能是reason。why可用for which代替。
Is this the reason wh...

个人认为 定语从句是完整句子，不缺主语及宾语时用

the reason为先行词的定语从句：
the reason why... = the reason for which...
the reason that... = the reason which...