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. a) as a method of the extraction of minerals, it was well establishedb) as a method of the extraction of minerals well establishedc) was a well-established method of mineral extractiond) was a well-established method of extracting mineral that wase) had been a method of mineral extraction, well established