Question

why的用法？

为什么
Is that the reason_________you are in favour of the proposal?选why
The reason is______he is unable to operate the machine.选that

Answer 1

作为关系副词 的why 引导定语从句时= for which
第一句 是定语从句 why 引导定从 并作 定从中的状语 = for which
也就是 you are in favour of the proposal for the reason

第二句 填that 这是表语从句
that he is unable to operate the machine.就是 the reason本身
why 也可以引导表语从句中 但意思不同 且主语不能是 the reason
如 the question is why he is unable to operate the machine.

Answer 2

第一句是定语从句，the reason 回到从句you are in favour of the proposal中作原因状语
第二句是表语从句

Answer 3

The reason is Why he is unable to operate the machine.
这个句子从语法结构上讲，是没有错的，但从意思上讲，就是逻辑混乱，这么说话的人肯定脑子有问题，所以老外从不这么表达的。以下用情景来解答：
他迟到了。
他为什么迟到？Why is he late?
理由：发生交通事故了。met an accident

That is the reason why he was late. 这里的THAT指的是发生交通事故了.这句话可以如下两个说法：
That is why he was late. 或 Meeting an accident is the reason why he was late.

第二句：The reason is ...意思是这理由是.. 当然是碰到交通事故。就是The reason is that he met an accident. 显然是不能说The reason is why he was late.(这理由是他为什么迟到。理由在哪里？）