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
KEY: C
我選E 想請問時態問題
我對題意的理解是-->
leaching"從18世紀一直到25年前"一直是well established的
是不是我哪裡理解錯誤呢??
還是題目的意思只有"在18世紀當時"leaching是well established的