the reason why is that什么从句

why引导定语从句，修饰先行词the reason，that从句在系动词is后面作表语，为表语从句，例如：

The reason why he is absent from school today is that he is badly ill and is in hospital. 他今天没来上学是因为他病得严重，并住院了（本句中，why he is absent ……today作reason的定语，为定语从句，that he is……hospital作is 的表语，为表语从句）

是原因状语从句，例如：

1、The reason why is that you all are my first students.因为你们是我带的第一批学生。

2、Part of the reason why is that， particularly when talking to journalists， the businesspeople or politicians tend to regard those conversations as off the record.之所以这样，部分原因是因为商界人士或政客们往往认为走廊里的谈话不会见诸报端，与记者的谈话尤其是这样。