the reason引导的从句什么时候用because什么时用thatthe reason why he was late was__he was caught in heavy traffic
问题描述：
the reason引导的从句什么时候用because什么时用that
the reason why he was late was__he was caught in heavy traffic
答
the reason why he was late was that he was caught in heavy traffic
这边是一句定语从句套上表语从句
【the reason why he was late】定语从句
【was that he was caught in heavy traffic】是一句表语从句
表语从句只能用that引导的