短語(yǔ)詞組短語(yǔ)corner coal pillar working face 邊角煤柱工作麪roof coal working face 放頂煤工作麪multidrill cutting coal working face 多孔鑽式割煤機(jī)coal pillar at working face 麪內(nèi)煤柱 返回 coal working face