炼

例句：

1. 1. The steel is being refined to improve its quality.
   钢铁正在被精炼以提高质量。
2. 2. He has been training for the marathon for months.
   他已经为马拉松训练了好几个月了。
3. 3.The gold was refined from ore by a skilled craftsman.
   金是从矿石中提炼出来的，由一位熟练的工匠完成的。