Ppbv
abbr. parts per billion by volume 十亿分体积比
🗣️ 情景例句
Keep right unless overtaking.
要靠右驾驶，除非超车。
How are you today?
今天还好吗？
suggested an idea on which he had been working for many years to the British Government and industrial circles.
他向英国政府和工业界提出了他研究多年的一项计划。