复句也叫复合句。
英语按句子的结构可分三种：
1）
简单句：只有一个主语（或并列主语）和一个谓语（或并列谓语）。
He often reads English in the morning.
Tom and Mike are American boys.
2)
并列句：由
并列连词（and, but, or等）或分号（；）把两个或两个以上的简单句连在一起构成。
You help him and he helps you.
The future is bright; the road is tortuous. 前途是光明的，道路是曲折的。
3）复合句：含有一个或一个以上从句的句子。复合句包含：名词性从句（主语从句、
宾语从句、表语从句和同位语从句）、
定语从句和状语从句等。
The foreign visitors took a lot of pictures when they were at the Great Wall.
Who will go to the conference is not important.