短语词组短语gassy y seam 瓦斯煤层thick gassy coal seam 含瓦斯厚煤层high gassy coal seam 高瓦斯煤层high gassy seam 高瓦斯煤层gassy seam mining method [矿业]瓦斯煤层采煤法 返回 gassy seam