But no evidence demonstrates that the duration of outdoor exposure - in places where people can move freely about - is long enough to cause substantial health damage.
但还没有证据表明，当人在户外自由移动时，身体接触到的烟气的残余，确实多得能够伤害健康。
But after a few days they arrive at an altitude, about 125km up, which is so rarefied that an ion can move freely about.
但几天之后，它们会达到大约125km的高度，在这里空气稀薄到使离子可以自由的运动。
But after a few days they arrive at an altitude, about 125km up, which is so rarefied that an ion can move freely about.
但几天之后，它们会达到大约125km的高度，在这里空气稀薄到使离子可以自由的运动。
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