标题: GWD－TN－8 Q31题求解 [打印本页] 作者: 风林火山 时间: 2009-11-24 14:35 标题: GWD－TN－8 Q31题求解 GWD-10-Q31 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 答案选C，我选E。大家能说说为什么嘛，答案对嘛？作者: cx_ding 时间: 2009-11-24 14:45
楼主为什么用过去完成时呢？