GMAT Sentence Correction (SC) | Re: Leaching, the recovery of copper from the drainage water of

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 established---'leaching and it' makes it an error of double subjecting with a single verb
B. as a method of the extraction of minerals well established -- This is a
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