有些矿井利用大气压力差引起空气自然流动，有些矿井则必须用扇风机把空气压人井内。
In some cases the difference in atmospheric pressure causes the air to circulate naturally; in others a fan must be used to pump air into the mine.
有些矿井利用大气压力差引起空气自然流动，有些矿井则必须用扇风机把空气压人井内。
In some cases the difference in atmospheric pressure causes the air to circulate naturally; in others a fan must be used to pump air into the mine.
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