一、the reason why肯定是定语从句 二、the reason that 不一定都是定语从句,分以下两种情况 1.当that后面加的句子是完整的句子的话,那它肯定是同位语从句,例如 He gave me the reason that he got up too late this morning. 2.当that 后面加的句子是不完整的句子的话（也就是缺少主语、宾语或表语时）,那它就是定语从句了,例如 I believe the reason that he gave. He gave me the reason that was unbelievable.(他给了我一个令人难以置信的解释
