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。
To move about or flow freely, as air.
像空气或液体一样自由流动。
To move about or flow freely, as air.
像空气或液体一样自由流动。
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