这一题有些疑问,答案说事C. 就算是没错,但是感觉上 E 也可以啊?难道是 well established as early as 18th century 是 fragment ?
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
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