Their task is very much, but they breathe in the oxygen supply is limited, only enough to use for four hours.

他们的任务很多，但是供给他们呼吸的氧气却很有限，只够使用四个小时。

youdao

To digress for a moment, it was biologist Felix Meerson who showed that high-altitude chambers where oxygen supply is limited, triggers an adaptive response that produces humans with profound mental capabilities and resistance against disease.

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