be动词的作用及用法是什么?

be动词的用法
英语的“be”是个特别动词；有些语言,如中文和马来文,并没有“be”这样的动词.
“Be”除了原形的“be”之外,还有另外七种形式：am, is, are, been, being, was, were.
在句子中,“be”可以是主动词(The Principal Verb)或助动词(The Auxiliary Verb).
当主动词时,“be”在性质上属于接系动词(The Linking Verb), 后面要有名词、形容词、地方副词或短语作补足语(The Complement).例如：
1. The man is a science teacher.
2. Mary's new dresses are colourful.
3. I have been there before.
4. Mother is in the kitchen now.
这四个都是陈述句,可以变成疑问句,方法简单,把主语和“be”或助动词对换位置即可：
5. Is the man a science teacher?
6. Are Mary's new dresses colourful?
7. Have I been there before?
8. Is mother in the kitchen now?
当“be”要在祈使句中出现时,它必须借重助动词“do”或“don't”之助,如：
9. Don't be silly!
10. Do be obedient!
11. Don't be a fool!
“Be”有两种缩写法,如下：
12. He's not./He isn't.
13. You're not./You aren't...
但“am + not”的缩写法只有一个：
14. I'm not.
有人用“ain't”, 但这并不是标准英语.
谈过了“be”作主动词的功能,现在看看“be”作助动词时,有些什么用法：
1.“Be + 现在分词”以组成进行式时态(Continuous Tenses),如：
15. Tony's maid is washing his new car.
16. The children are playing in the field.
17. Samuel was eating when I came in.
18. We have been living here since 1959.
2.“Be + 过去分词”以组成被动语态(The Passive Voice),如：
19. Her money in the drawer was stolen.
20. A number of good jobs are taken up byforeigners.
21. David studied in * but has been trained as a language lecturer in America.
22. Can all the wonderful birds be found in our Bird Park?
23. The disobedient boy was told to stand out- side the classroom.
24. Steps are being taken to reduce traffic con- gestion during peak hours.
25. Dishonest students will be immediately dealt with.