泛指某一类人、事、物，相当于any
The best way to learn a language is to live among its speakers.
I know that the pressure to stay slim is a problem, especially for an actress.
泛指某人或某物，但不具体指明何人或何物，相当于a certain或some
A John called you just now.
There is a car in the yard.
表示数量，有“一”的意思，相当于one
A bird in the hand is worth two in the bush.
I need a student to help me.
表示“每一”，相当于per
The Chinese Export Commodities Fair is held in Guangzhou twice a year.
The car is travelling at 100 miles an hour.
用在序数词前，表示“又一，再一”
A second plan was devised and is now going forward.
Please give me a second chance.
抽象名词表示一个具体情况，一个具体动作
Their performance became a success.
Sometimes disappointment can make you feel like a failure.
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