Ppm.
[医] 兆比率(百万分之几)
🗣️ 情景例句
First round's on me.
第一轮我请客。
Birds of a feather flock together.
物以类聚，人以群分。
but we found that it traced its way through the trees.
没想到它到树林中继续向前延伸。