be动词的形式：
be，is，am，are，was，were，being，been
例句：
The man is back.
They are back.
He was back.
They were back.
They have been back.他们已经回来了。
be动词的用法：
后面接名词、形容词、地点副词或短语作补足语。
The man is a teacher.
a teacher 为补足语，对man的补充说明。
is为连接主语和补足语的成分。
Mary's new dresses are colorful. 玛丽的新裙子是五颜六色的。
同上，colorful为补足语
My mother was in the kitchen.我的妈妈再厨房里。
总结：be动词就是起联系作用，起到连接主语和补足语的作用。
练习：
他们是老师。They are teachers.
他以前是一名老师。He was a teacher before.
他已经当了3年的老师。He has been a teacher for 3 years.
be动词的否定：
在 am，is，are，was，were后面加not。
缩略式 am not，isn't，aren't，wasn't，weren't。
am，is，are是现在时，was，were为过去时。
The man isn't back. 那个男人没有回来。
I am not back. 我没有回来。
They aren't back. 他们没有回来。
以上为现在时
He wasn't back. 他没有回来。
They weren't back.他们没有回来。
以上为过去时
be动词的提问和回答：
be动词变疑问句，把be动词提到句首，其他成分保持不变。
Is he a teacher? Yes,he is./No,he isn't.
他是一名老师吗？是的，他是。/不，他不是。
Are you a teacher? Yes,I am./No,I am not.
你是一名老师吗？是的，我是。/不，我不是。
Were they teachers? Yes,they were./No,they weren't.
他们以前是老师吗？是的，他们是。/不，他们不是。
练习：
1、他是医生吗？Is he a docotor?
不，他不是。No,he isn't.
2、他们昨天在教室吗？Were they in the classroom yesterday?
是的，他们在。Yes,they were.
造句：
他们昨天不在教室。
答案：They weren't in the classroom yesterday.
