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
给的答案是C,但也有不少人支持E,反对E的是说没有必要用过去完成时,那eighteenth century明显在25 years ago之前,就是该用过去完 成时嘛
[此贴子已经被作者于2006-9-17 19:50:46编辑过] |