系動詞Be(am, is, are)的用法
基本形式：am、are、is
1、am
第一人稱I+am (注意：“I”無論何時都要大寫，不管位于句首還是句中).
例：I am a beautiful girl. I am twenty.
I am 還可縮寫成I'm。 如：I'm David. 我是大衛(wèi)。
但是am與not不能縮寫。
2、are
第二人稱you+are; 一人稱復(fù)數(shù)we+are; 三人稱復(fù)數(shù)they+are 其他復(fù)數(shù)名詞+are。
(注意：第二人稱單復(fù)數(shù)同形，都為you)
例：You are my good friend. We are in the same class.
They are on the road. The books are on the desk.
are與主語還可縮寫。如：
We are= We're， They are =They're, You are = You're。而are與 not可縮寫成aren't。
3、is
第三人稱he(男) +is ; she(女)+is; it(不是人)+is;其他單數(shù)名詞+is。
例：HeShe is a good student. It is a white cat. A dog is on that street.
is也可與主語縮寫,如:
He is = He's, My mother is = My mother's等。但是This is不可縮寫。而is與not可縮寫成 isn't。
如:This isn't a book. 這不是一本書。