is的用法：
第三人稱he(男) +is ; she(女)+is; it(不是人)+is;其他單數(shù)名詞+is
例句：
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。