短语词组短語coal -mining methods 採煤方法coal surface mining 露天採煤single coal seam mining 單一煤層開採coal resources mining 煤炭資源開採coal pillar mining 帶煤柱開採coal mine mining 鑛井開採coal caving mining 煤採煤;放頂煤開採;放頂煤opencast coal -mining 露天採煤 返回 coal mining