clauses and use them freely
课前自学（ SB P20-21 Discovering useful structures）
语法知识精讲
1．表语从句在复合句中作主句的表语。引导表语从句的连接词有：that ,whether, as if（仿佛）；连接代词有who, whose, what, which,连接副词有 when, where, how, why等。另外as, because，也可引导表语从句。表语从句位于连系动词后，有时用as if引导。其 基本结构为：主语+系动词+从句。
常见的表语从句的句型有
This is because…
The reason for …(why) is that…
He\ She looks as if …
The trouble\problem is that…
例如:
