单项选择题
A.呼喊、敲击 B.掘小巷 C.打钻 D.放顶
A.为零 B.中间 C.最低 D.最高
A.3% B.5% C.20% D.40%
A.CH4＜1% B.CH4＜1.5% C.CH4≤0.5% D.CH4≤1%
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