1.指一类人或事

A plane is a machine that can fly.

2.第一次提及某人某物，非特指

A boy is waiting for you.

3.表示“每一”相当于 every, one

We study eight hours a day.

4.表示“相同”相当于 the same

We are nearly of an age.

5.用于人名前，表示不认识此人或与某名人有类似

性质的人或事

Mr. Smith came to visit you when you were out. That

boy is rather a Lei Feng.

6.用于固定词组中

a bit, once upon a time, in a hurry, have a walk

7.用于 quite, rather, many, half, what, such 之后

This room is rather a big one.

8.用于 so (as, too, how)+形容词之后

She is as clever a girl as you can wish to meet.

9.用于 most 之前，意思是“非常”

It is a most useful dictionary.

10.用于序数词前，表示“又一”，“再一”

Can you give me a second chance?

11.用于抽象名词前，使之具体化，表示与之相关的

具体的人或事

He was a success in business.