句子构成的成分共分为九种：主语，谓语，宾语，表语，定语，状语，补语，同位语和插入语。

一、主语：句子的核心主体，通常位于谓语动词之前，表明一个句子是谁或何种情况所发出执行或是承受的。在雅思写作中常做主语的有名词、代词、主语从句、V-ing 、To do五种。

1、名词：Computers are now being widely used in almost all fields.

2、代词：We are now living in an information-explosion era.

3、主语从句：Whether sports stars should earn a high salary is still discussed heatedly.

4、V-ing: Surfing the Internet offers a new way for people to relax themselves.

5、To do: To protect the environment is everybody’s business.