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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: as early as the eighteenth century 作为一个 状语修饰主句，表明什么时候成为一个方法；
D: as early as the eighteenth century 作为一个定语修饰方法；
显然，这个语境中as early as 作为状语更合适
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