请教GWD-1-41

msyefu

为什么不选E？用过去完成时？

carolhide

最好把题贴出来，方便别人讨论。你问的应该是这题吧？

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.

1. as a method of the extraction of minerals, it was well established



2. as a method of the extraction of minerals well established



3. was a well-established method of mineral extraction



4. was a well-established method of extracting mineral that was



5. had been a method of mineral extraction, well established

答案是C，看它的时间状语as early as the eighteenth century所以是过去时而不是完成时了。意思是早在18世纪。