表语从句位于主句系动词之后，可分为两类：be + that型从句和be + 疑问词型从句。
1. be + that型从句
eg. The fact is that we have no idea to solve this problem.事实就是我们没办法解决这个问题。
The reality is that the party must be cancelled because of the storm. 现实就是因为暴风雨这个聚会必须得取消了。
2. be+疑问词型从句
eg. The question is whether they will help us. 问题是他们会不会帮我们。
The problem is why she didn't go back home directly. 麻烦就麻烦在为什么她没直接回家。
3. 表语从句使用陈述语序。
eg. The question is when he can arrive at the hotel. 问题是他什么时候能到酒店。
4. 主句主语是reason时，表语从句要用that引导，不可用because。但reasons作主语时，表语要用名词短语并列。
eg. The most common reasons for ...... are 名词短语1，名词短语2 and 名词短语3。
