Ppb
[化] 十亿分率
🗣️ 情景例句
What's going on?
你在忙些什么？
Paul started with surprise when Jim tapped his shoulder.
当吉姆拍了保罗的肩膀时，保罗吓了一跳。
We've got to do something about the neighbor's dog!
我们得对邻居的狗采取点行动了！