niobium extraction by converter blowing

例句：

1. 1.The process of extracting oil from the earth is called drilling.
   从地下提取石油的过程被称为钻探。
2. 2. The extraction of methane gas from shale rock is a promising field for energy research.
   从页岩岩石中提取甲烷气体是能源研究的一个有前途的领域。
3. 3. The extraction of oil from the ground has been a major industry in many countries.
   从地下提取石油一直是许多国家的主要产业。