The main reason why he lost his job was that he drank.是定语从句还是同位语从句?

问题描述:

The main reason why he lost his job was that he drank.是定语从句还是同位语从句?

前半部分是关系副词why引导同位语从句 ,解释reason.that he drank.这部分是表语从句.