A.煤層產(chǎn)狀發(fā)生顯著變化 B.煤層結(jié)構(gòu)發(fā)生變化 C.瓦斯涌出量明顯變化 D.頂?shù)装鍘r石裂隙顯著變化
A.第三紀(jì)(R) B.三疊紀(jì)(T)至侏羅紀(jì)(J) C.石炭紀(jì)(C)至二疊紀(jì)(P) D.寒武紀(jì)(∈)至奧陶紀(jì)(O)
A.植物條件 B.氣候條件 C.地理?xiàng)l件 D.地殼運(yùn)動(dòng)條件