系动词之后的是表语，所以系动词之后的是表语从句 系动词包括
一 be动词类：am、 is 、are 、was 、were 二 变化类：become、 get 、 turn 、 grow 、go 三 感官类:look 、sound、smell、taste、feel 四 延续类 ：remain 、stay 、keep 五 似乎类：appear、seem、look
举例:
The problem is who can drive the bus. His suggestion is that we (should) have a meeting this afternoon.
Spring is when the flowers bloom.
其他动词之后的宾语为一个句子时，称之为宾语从句 :
We all know that he has studied English since 1998.
I will like whatever you give to me on my birthday.
