例如:—Who is he?—He is Tom’s father.—What’s this?—It is a book.are用于第二人称单、复数和第一、三人称的'复数。例如:You are a student. We are students, too.
2、am,is和are可以帮助构成否定句和疑问句。在am,is或are之后加上not,即将句子变成了否定句；把be动词提到句首,即将句子变成了疑问句。
例如:I’m from China. →I’m not from China. →Are you from China? (对I am的提问比较特别)
He’s thirteen years old.→He isn’t thirteen years old.→Is he thirteen years old?
They are policemen. →They aren’t policemen. →Are they policemen?
看了以上例句,一定要注意am,is和are在句中的缩写形式。另外,am,is,are与this,these,those在一起时一般不缩写。
3、be也可以位于句首,表示向别人提出要求。例如: Be a good student! 做个好学生！