1、主语（subject）：表示句子描述的是"谁"或"什么"，通常是谓语动词的动作执行者。通常有名词、代词、数词、动词不定式、动名词、从句等充当。

The students worked very hard.

They are from America.

80% of the students in our class are girls.

To learn English is very difficult for us.

　　=It is difficult for us to learn English.

Swimming in the lake is dangerous.

What he said is true.

2、谓语动词：什么主语的动作或具有的状态与特征。

构成形式如下：

1）简单谓语：由一个动词或动词短语构成。

She practices speaking English every day.

The woman takes good care of the baby.

I have got rid of smoking.

2）复合谓语形式1：由情态动词或助动词+动词构成。

You may go now.

He has caught a bad cold.

We are going to visit the old town tomorrow.

3）复合谓语形式2：由系动词+表语构成。

We are students.

She becomes famous.

The little girl is afraid of the snake.

4）复合谓语形式3：情态动词+系动词+表语

It will be wasted.

He must be wrong.

We will be free tomorrow.

5）复合谓语形式4：被动句的谓语动词。

Mary was seen to swim across the river.

They were expected to finish the work as soon as possible.

3、表语：用来说明主语的身份、特征和状态的成分。一般在系动词之后。

表语可由下列结构充当：名词、代词、形容词、分词、数词、不定式、动名词、介词短语及表语从句。

The young man has turned thief.

All of these are yours.

The flower is beautiful.

The film is moving.

We are moved by the film.

Her job is to look after the baby.

　　My job is teaching English.

　　Tom was out then.

　　The fact is that he passed the exam successfully.

4、宾语：表示动作承受的对象。可由下列结构充当：名词、代词、数词、动名词、不定式、宾语从句等。

He bought a new car.

The heavy snow prevented her from going to school.

She enjoys listening to music.

I don't know how to get there.