1.The company envisioned opening the sides of two mountains to extract coal.
这家公司打算挖开两座山的山坡采煤。
2.Miners had to dig deeper to extract coal, which became uneconomical.
为了提高产量，矿工不得不向更深处挖掘，这变得越来越不合算。
3.Design of the Hydraulic System of Extract Coal Filter Press
压滤机液压系统设计
4.Study on Technique to Extract Coal and Coke Together
煤焦共采采掘工艺初探