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　　2、在句子中，be有两种主要作用：一是作为系动词(The Linking Verb)，本身可以作用谓语动词；二是做为助动词(The Auxiliary Verb)，与谓语动词一起构成各种时态和被动语态等。

　　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.