1、a/an用在单数可数名词前面,表示这个人或事物是泛指的不确定的一个,相当于中文的“一个”。通常在第一次提到某人或某物时用a/an
I gave him a book yesterday.
There is a tree in front of my house.
用在不可数名词前面意义上也有变化如wood木头,a wood一片树林power威力,a power大国/beauty美丽,a beauty美人,a strong wind一阵强风
2、a用在读音为辅音开头的名词之前,而an用在读音为元音开头的名词之前。例如:a university(虽然u是元音字母,但不读元音。)an hour(虽然h不是元音,但单词读音是元音开头)
3、用其中的任何一个,代表他们所属种类的特性。
A horse is useful to mankind.马对人类有用。
A bird can fly.鸟会飞。
4、用在事物的度量单位前,如时间、速度、价格等,表示"每一个"。
We often go to school two times a day.
I went to the library once a week at least.
5、用于某些特定的词组。例如:a few几个,a little有点,等等。
She has a few friends in this city.
There is a little milk in the bottle.
当有such what many so how too quiet rather very修饰时
He left in such a hurry that he forgot to close the door.
What an interesting book it is!