a

一、一个用于可数名词单数前

She adopted a cat from the shelter last month.

她上个月从收容所领养了一只猫。

每

He goes swimming three times a week.

他每周去游泳三次。

某个、某位

A Mr. Lin called while you were out.

你外出时有位林先生打过电话来。

一种、一类表示种类

This is a cheese I have never tasted before.

这是一种我以前没吃过的乳酪。

字母A

The word "apple" begins with a lowercase a.

apple 这个词以小写字母 a 开头。

优等、甲等成绩

She got an A on her history essay.

她的历史论文拿到了优等。

A型血型

My blood type is A, the same as my mother's.

我的血型是A型，跟我母亲一样。

A音音乐

The orchestra tuned to an A before the concert.

乐团在音乐会前依A音调音。