在英语语法中，be动词意思和用法很多，一般的意思是：是，此种用法，有多种变化形式，is，am，are，was，were，being，been，to be.另外，be动词还有成为的意思。根据句子中不同的人称、数和时态，应该选择相应的be动词
be （be/is/are/am/was/were)
[bi:]
vi
he is, we are, you are, they are （缩略式 I'm, you're, he's, we're, you're, they're）, （否定缩略式 I'm not, isn't, aren't）, 过去时 I was, you were, he was, we were, you were, they were （过去时否定缩略式 wasn't, weren't）,过去分词been,现在分词being
英语的“be”是个特殊动词；有些语言，如马来文等，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)
例句对照
编辑
【当做主动词时，“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：
The man is a science teacher.
这个男子是一位科学教师。
Mary's new dresses are colourful.
玛丽的新衣服色彩鲜艳。
I havebeen there before.
我以前去过那里。
My motheris in the kitchen now.
我妈妈现在在厨房里。
★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：
Is the man a science teacher?
Are Mary's new dresses colourful?
Have I been there before?
Is mother in the kitchen now?
★当“be”要在祈使句中出现时，陈述句可借助助动词“do”，否定句必须在前加上助动词“don't”，如：
Don't be silly!
Do be obedient!
Be careful!
Don'tbe a fool!
★“Be”有两种缩写法，如下：
He's not...../He isn't....
You're not...../You aren't...
★但“am + not”的缩写法只有一个：
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
【1.】“Be + 现在分词”以组成进行式时态(Continuous Tenses)，如：
Tony's maidis washing his new car.
The children are playing in the field.
Samuel was eating when I came in.
We have been living here since 1959.
【2.】“事/物人 +Be + 过去分词”以组成被动语态(The Passive Voice),如：
Her money in the drawer was stolen
A number of good jobs are taken up by foreigners
David studied in Taiwan but hasbeen trained as a language lecturer in America
Can all the wonderful birds be found in our Bird Park
The disobedient boywas told to stand out- side the classroom
Steps are being taken to reduce traffic con- gestion during peak hours
Dishonest students will be immediately dealt with
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