下面做个简要的讲解。

一、be 动词做系动词

1、系动词+表语”的结构

当be 动词做系动词使用时，主要构成“系动词+表语”的结构，在句子中做谓语。表语可以是名词、形容词、副词、介词短语等。例如：

The man is a science teacher.

Mary's new dresses are colourful.

Mother is in the kitchen now.

I have been there before.

They shall be here at 10:00 tommorow.

That can't be true.

You are not being very polite.

Your brother is being very annoying this evening

2、be 动词的一般疑问句，方法是把be 移到主语前面，也可说成是移到句首。

Is the man a science teacher? Yes, he is. / No, he isn't.

Are Mary's new dresses colourful? Yes, they are. / No, they aren't.

Was mother in the kitchen then? Yes, she was. / No, she wasn't.

Were you at home the day before yesterday? Yes, I was. / No, I wasn't.

Was she late this morning? Yes, she was. / No, she wasn't.