GWD1-Q41:

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和E选项感觉不适很清晰，帮忙分析一下，thanks!

C和E选项感觉不适很清晰，帮忙分析一下，thanks!

当时偶做这道题的时候，上来就排除E了，

上课的时候，老师应该说所过去完成时不太使用，要谨慎~~看前后有没有表示过去的过去的标志

具体过去完成时的使用，你可以仔细阅读下OG前面讲解时态的部分，那上面讲的很清楚.

可能还有其他解释，请高手补充~~

as early as the eighteenth century是修饰established的

而不是method of extracting mineral ，所以不能做定语从句。逻辑上不通