请问天山新题20-5#
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 taken 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(C)
(E) had been a method of mineral extraction, well established
答案是C,我选了E,请问为何选C?
若选C,as early as修饰什么?
[此贴子已经被作者于2005-9-8 10:55:58编辑过] |