二、简单句的核心变化

简单句的核心变化其实就是 一主一谓（n. + v.） 表达一件事情，谓语动词是其中最重要的部分，谓语动词的变化主要有四种：三态加一否（时态、语态、情态、否定），其中时态最重要。

简单句除了谓语动词的变化以外，还有主语/宾语/表语的变化

1、主语/宾语/表语通常情况下都是由名词/代词或由其构成的短语充当的

Most graduates always want a big-firm job.
主语：大多数毕业生，名词短语
宾语：大厂工作，名词短语

She is the leader of the organization.
主语：她，代词作主语
表语：领导者，名词作表语
主系表结构

They gave us a good impression.
主语：他们，代词作主语
双宾语：我们(代词)、一个好印象(名词词组)

2、doing(动名词)/to do(不定式)充当主语

只要把动词变成dong/to do的形式，就可以相当于名词来使用，就可以做主语/宾语/表语

Laughing probably has great influence on health. doing作主语，笑可能对健康由利
To laugh probably has great influence on health. to do作主语，笑可能对健康由利
上面两个句子是等价的关系

doing和to do本质是一样的，有点小区别在于：dong作主语常在居首，to do作主语常放在句尾，主语比较短的时候还可以，但to do作主语过于长的话，放在句尾有点别扭，故出现了it形式主语。即：
lt probably has great influence on health to laugh.

doing/to do作主语的时候，不一定只有它们这一个或者两个词，也有可能是一个长的词组
若是及物动词形式，就可以接宾语

Laughing probably has great influence on health.
Having only a foggy view of the future is of little good.

lt probably has great influence on health to laugh.
lt is no use to talk about dreams without trying.

总结：doing/to do都可以作主语，但不一定只有一个词，有可能是及物动词后跟一个词组等，或者加上修饰限定等成分构成的短语整体作主语

2、doing(动名词)/to do(不定式)充当宾语

We enjoy reading books in the library.
doing动名词作宾语
enjoy doing sth. enjoy后面只能接doing

The members of the board decide to vote against the new plan.
to do不定式作decide的宾语

3、doing(动名词)/to do(不定式)充当表语

Our main goal is to finish the task on time.
to do不定式作系动词is的表语

4、多个主语/宾语/表语并列

Science and technology will develop the process of society.
两个名词并列作主语。科技将推动社会发展

Social science disciplines include geography, economics political science and psychology.
多个名词并列作宾语

That doesn’t mean sitting down and doing nothing at all.
mean后跟了两个并列的宾语(doing动名词作宾语)