The stratosphere holds an natural amount of ozone, but by Earth's surface this becomes air pollution.

大气平流层中存在有大量的臭氧，它们若是在地球表面则会造成空气污染，空气中的臭氧会严重破坏人的肺部。

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Scientists say that despite the widely held belief we need eight hours of sleep a night, six to seven hours is the natural amount.

尽管大多科学家都坚信一天需要睡八个小时，但是六个小时就已经是自然睡眠的足够时间了。

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Scientists say that despite the widely held belief that we need eight hours of sleep a night, six to seven hours is the natural amount.

尽管大多科学家都坚信一天需要睡八个小时，但是六个小时就已经是自然睡眠的足够时间了。

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What, then, is the natural amount of money required?

FORBES: Yes, Printing Money Can Create Wealth

As you all know, natural gas is -- a growing amount of natural gas, the reserves, because of the ability to frack shale rock, has been increasing.

WHITEHOUSE: Press Briefing

Although you went on to recognise that human activity causes these natural flows to become unbalanced, it can actually take only two or three decades for humans to cumulatively emit an amount that matches those natural fluxes, given how long carbon dioxide persists in the atmosphere and the low amount that the earth can absorb each year.

ECONOMIST: Letters