the reason that引导从句,如何判断为定语从句和同位语从句呢

She didn’t answer for the simple reason that she couldn’t think of anything to say.这句话是同位语从句,为什么?
the reason why``` is because 和the reason why```is that 的用法有区别吗?

that 既可引导同位语从句又可引导定语从句,其区别在于：1.同位语从句由连接词that引导,连接词that本身无意义,在同位语从句中不充当任何成分,不可省略,不可以用其他词替代；2.定语从句由关系代词that引导,关系代词that在从句中充当一定的成分,作宾语时可省略.参考美国传统词典because词条的特别说明：

Usage Note:A traditional rule holds that the construction "the reason is because" is redundant,and should be avoided in favor of "the reason is that." The usage is well established,however,and can be justified by analogy to constructions such as "His purpose in calling her was so that she would be forewarned of the change in schedule" or "The last time I saw her was when she was leaving for college".All three constructions are somewhat less than graceful,however.

可见,专家们想让人用 is that ,但是 is because 的用法已经摆脱了语法的束缚,成为既成事实了.