Leaching, the recovery of copper from the drainage water of mines, as a method of the extraction of minerals, it was 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.
- as a method of the extraction of minerals, it was well established
- as a method of the extraction of minerals well established
- was a well-established method of mineral extraction
- was a well-established method of extracting mineral that was
- had been a method of mineral extraction, well established
答案：C.Mine 一到这种意思差不多的时候我就分不清楚。没找到以前有人问这个。
还有十几天就考试了。觉得CD上大家都好强啊，一套卷子下来错的都是10道以内的。。。再看看自己，大哭~ | 
