原题最后的正确句子是(括号里是划线部分) Leaching, the recovery of copper from the drainage water of mines, (was a well-established method of mineral extraction) 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.
其他的选项明显不对就不写出来了,但是解释里说“as early as the eighteenth century副词性短语修饰but前的分句”完全不明白。
原句简化后就是Leaching(was a well-established method of mineral extraction) 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.