Usages of bēi
你 要 一 杯 水 吗？nǐ yào yì bēi shuǐ ma?
Do you want a cup of water?
我 不 要 水，我 要 一 杯 茶。wǒ bú yào shuǐ,wǒ yào yì bēi chá.
I don’t want water; I want a cup of tea.
我 去 食堂 吃饭 的 时候， 顺便 帮 室友 带 了 一 杯 咖啡。wǒ qù shítáng chīfàn de shíhou, shùnbiàn bāng shìyǒu dài le yì bēi kāfēi.
When I went to the cafeteria to eat, I also brought a cup of coffee for my roommate.
我 去 公园 散步 的 时候， 顺便 买 一 杯 咖啡。wǒ qù gōngyuán sànbù de shíhou, shùnbiàn mǎi yì bēi kāfēi.
When I go to the park for a walk, I also buy a cup of coffee while I’m at it.
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