对GWD-1-Q41答案的疑问

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

正确答案是C，但mineral extraction后面紧跟as early as the eighteenth century不会有修饰mineral extraction的嫌疑吗？

看了前辈们的讨论帖，E时态错是不是因为leaching有可能从eighteenth century直到25years ago都被使用，所以不能过去完成要用过去？

要用过去完成时，一定要表达的是A事件发生在过去的B时间之前。

如果你想说，leaching在人们发明 XXX方法之前一直都是提炼方法，则可以用过去完成时。

我觉得这个句子没有哪里表明作者想要比较leaching和另外一件事情的先后顺序。

谢谢skyzhang gg！

还是觉得mineral extraction后面紧跟as early as the eighteenth century会有修饰mineral extraction的嫌疑...

有好心人指点一下吗？