196. 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
B. as a method of the extraction of minerals well established
C. was a well-established method of mineral extraction
D. was a well-established method of extracting mineral that was
E. had been a method of mineral extraction, well established
C is correct.
我选的是E，在看到E之前我觉得C的表达很清晰很简洁，但是有比较之后我觉得E更好一些。
首先我觉得early这个短语修饰的是establish还是extraction并没有一定，而原句是修饰establish的。
其次整个主句发生的时间都在but从句之后，but从句用得是一般过去时，E用过去完成时在时间概念上的表达不是更清晰么？
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