why 引导的是标语从句.
二、由连接代(副)词引导的表语从句
连接代词who,whom,whose,what,which,whoever,whatever,whichever；
连接副词where,when,how,why.
That was what she said this morning in her bedroom.那就是她今天早晨在卧室中说的.
that was why he did not come to your birthday party .那就是为什么他没有来你的生日party