题目选项分析

Leaching, the recovery of copper from the drainage water of mines, as a method of the extraction of minerals well established as early as the eighteenth century, but until about 25 years ago miners did not realize that bacteria take an active part in the process.

Leaching, the recovery of copper from the drainage water of mines, was a well-established method of mineral extraction as early as the eighteenth century, but until about 25 years ago miners did not realize that bacteria take an active part in the process.