英语语法分析

A backpack sends O2 in to let astronauts breathe normally.

一个背包可以输送氧气，让宇航员正常呼吸。

A large tree might make around 100kg of O2 per year.

一棵大树每年可以产生大约100公斤的氧气。

It takes about 7 to 8 trees to make enough O2 for one person to breathe for a year.

大约需要7到8棵树产生足够一个人呼吸一年的氧气。