Get detailed explanations to advanced GMAT questions.
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
Option C is the correct answer.
Concept tested: Sentence fragment, modifiers, tenses.
A) This is a sentence fragment. Moreover, it uses the pronoun “it” which is ambiguous.
B) Sentence fragment.
C) Correct Answer
D) Inappropriate usage of “That” as it refers to minerals.
E) Wrong tense. We do not require past perfect tense.