人活着必须呼吸氧气。

People must breathe oxygen in order to live.

它们与所有哺乳动物一样需要呼吸氧气。

Like all mammals, they need to breathe oxygen.

从你出生的那一刻起，你的身体就知道要呼吸氧气，排出二氧化碳。

From the moment you're born, your body knows that it has to breathe to receive oxygen and get rid of carbon dioxide.

有一些甚至连腮都没有，必须通过他它们极薄的皮肤，从水里直接呼吸氧气。

Some don't even have gills yet and must absorb oxygen directly from the water through their tissue-thin skin.