[观察例句]
1．The question is when he can arrive at the hotel.
2．The book is not what I need.
3．That is why she failed to pass the exam.
4．The trouble is that we have no money.
5．The argument is whether it rains tomorrow.
[归纳用法]
一、概念：
从句在整个主句中作表语，因此被称为表语从句。表语从句隶属于名词性从句。
放在系动词之后，一般结构是“主语＋系动词＋表语从句”，可以接表语从句的连系动词有be，look，remain，seem等
