求问一道语法题！

FreddyZ

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.

• Aas a method of the extraction of minerals, it was well established  分析A选项
• Bas a method of the extraction of minerals well established  分析B选项
• Cwas a well-established method of mineral extraction  分析C选项
• Dwas a well-established method of extracting mineral that was  分析D选项
• Ehad been a method of mineral extraction, well established  分析E选项
  

有大神知道为什么 A里面的it不能指代leaching么？

啊澄xi

it 那句话是一个完整的句子，leaching只有一个名词在那里，句子不完整....

Zweistein

试着回答，选C。

A. 逗号+but前后平行且都是独立句。此选项错在没谓语。

对于it.根据曼哈顿语法解释。it作为代词有两个作用：1.指代前面出现的单数名词；2.placeholder，基本无意义。
不管哪种，看到it前的逗号说明这是个非独立句。所以不能有it。另外前面有好几个单数名词，指代不明。
Tips: 根据经验，一般句中有it的都是错误选项。（前提是必须仔细分析，考试没时间的话可以直接排除。）
B. 同A.
C.Correct
D.句末that 指代不明，不知道是前面哪个名词。
E.两个谓语时态不平行。