今天来说一下表语从句，表语从句的结构为：主语+系动词+引导词+陈述句
系动词包括be、seem, 持续系动词stay、keep、remain, 感官系动词look、sound、taste、feel、smell, 变化系动词turn、get、become、grow等。
The place is where I was born .
The place 作主语，is是系动词，从句where I was born 作表语，主句主系表结构缺表语。
That is why you have to learn English well.
从句Why you have to learn English well 作表语
The question is whether we can get there on time.
从句whether we can get there on time作表语用陈述语序，表语从句只用whether, 不用if
The reason why he failed in the exam is that he was careless.
主句the reason 作主语，is 是系动词，从句that he was careless 作表语，why he failed in the exam 修饰名词the reason作定语
