055 问得好 Good question

A chemistry teacher told his friends,"Oxygen was not found until18 th century."

A friend asked,"So,what did people breathe before that"

一位化学老师对朋友们说:"氧气是在 18 世纪才被发现的。"

一位朋友问:"那么在那之前,人呼吸什么呢?"

chemistry n. 化学