Somehow, he'd managed to persuade Kay to buy one for him.

不管怎么说，他已设法说服了凯给他买一个。

《柯林斯英汉双解大词典》

Can I only buy one piece?

我可以只买一件吗？

youdao

Buy one, get the second one half off.

买一件，第二件就半价。

youdao

He says people buy one piece, or at most three pieces,each, not too much.

VOA: standard.2010.03.08

Each consumer is going to buy one product, either from Firm 1 or from Firm 2.

每个消费者会买一个产品,从公司1买或者从公司2买

耶鲁公开课 - 博弈论课程节选

I think I'm going to buy one, maybe next week.

我打算去买下那一顶，也许下周就去。

I like实战 - SpeakingMax英语口语达人

Cummings hopes to turn Bats into an exchange of its own, or to buy one.

FORBES: Magazine Article

Answer: C -- Only 35% of people who buy a hybrid once buy one again.

CNN: Hey Earthling, it's Earth Day; time for a quiz

"I can already buy one right now if I return my birthday presents, " he says.

WSJ: How I Spent My Allowance: Twins Buy Toys, but Help Cats, Too