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题库 / Prep2008E2-SC-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.
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
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C中as early as the eighteenth century作为状语，表示（早在18世纪时）leaching是方法，而D中that was as early as the eighteenth century是定语修饰method，表示leaching是（18世纪的）方法。我们一般说，早在某个时候，某物就已经是……
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