be動詞用法：
當做主動詞時，“be”在性質(zhì)上屬于接系動詞(The Linking Verb), 后面要有名詞、形容詞、地方副詞或短語作補足語(The Complement)。例如：
The man is a science teacher.
這個男子是一位科學(xué)教師。
Mary's new dresses are colourful.
瑪麗的新衣服色彩鮮艷。
I have been there before.
我以前去過那里。
My mother is in the kitchen now.
我媽媽現(xiàn)在在廚房里。
這四個都是陳述句，可以變成疑問句，方法簡單，把主語和“be”或助動詞對換位置即可：
Is the man a science teacher?
Are Mary's new dresses colourful?
Have I been there before?
Is mother in the kitchen now?
當“be”要在祈使句中出現(xiàn)時，陳述句可借助助動詞“do”，否定句必須在前加上助動詞“don't”，如：
Don't be silly!
Do be obedient!
Be careful!
Don't be a fool!
“Be”有兩種縮寫法，如下：
He's not...../He isn't....
You're not...../You aren't...
但“am + not”的縮寫法只有一個：
I'm not.