Ppb
[化] 十億分率
??? 情景例句
He worked his way through college.
他半工半讀念完大學。
An ounce of prevention is worth a pound of cure.
預防勝于治療。
The young man did not wake up until the bed had struck the ground.
那年輕人直到床撞到地上才醒了過來。