You might consider that we could pull back in one channel to see the effects of another.
你可以理解为我们从一个市场渠道上退下来，从而观察另一个渠道的市场效果。
This paper introduced the technical of using drilling downward hole from working surfale in protective coat bottom tu pull out goaf gas, and the effects were analysed and summarized.
前言： 介绍了在被保护层底板巷向保护层工作面施工下向穿层钻孔，抽采保护层工作面采空区瓦斯的具体做法，并对取得的效果进行了分析总结。
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