没有干净的空气，人类无法长期生存。

You cannot ___exist without clean air for an extended period.

在如此贫困的条件下，没有外部援助几乎无法生存。

It's nearly impossible to ___exist in such poverty without external aid.

一些微生物可以在深海热液喷口等极端环境中生存。

Some microorganisms can ___exist in extreme environments like deep-sea vents.