Ron说，E错在两点，第一：时态不对，过去完成时表示leaching是过去的办法，现在不用了，但句中并没有表述这种意识； 第二，well established不应该作为非必要修饰语，个人理解从这个句意出发，前半句说这个方法好，后半句说发现这个方法的缺点，well established作为非必要修饰语，就削弱了整个句子的转折意味。

(D) that可能指代method或mineral(根据逻辑含义选择指代对象)， 但修饰method和mineral句子逻辑意思都不对

D选项中that就近指代的是mineral而不是method

RON:
"essential vs. nonessential modifier".
NOTE: i've never seen this issue directly tested, so it's not important for you to be able to distinguish between the two -- the only thing that's important is for you to realize that both are ok, under certain circumstances

an "essential" modifier (which is NOT set off by commas) is a modifier that actually narrows or specifies the noun/action to which it's attached.
for instance:
our top student whose score fell below 50 received a consolation prize.
--> this doesn't refer to the top student among all of our students; this only refers to the top student among those whose scores fell below 50 points. therefore, we need the essential modifier (no commas) to narrow "our students" to "students whose score fell below 50".

a "nonessential" modifier (which IS set off by commas) is a modifier that does not narrow or specify the nouns/action to any greater degree than does the rest of the sentence; it merely provides more information about that noun/action.
for instance:
our top student, whose score fell below 50, received a consolation prize.
--> here, we are actually talking about our top student. the meaning of the sentence is that all of our students' scores were below 50, but at least our top student received a consolation prize.

(D) Importantly, in this sort of structure (NOUN1 + prep + NOUN2 + THAT..., or NOUN1 + (modifier ending with NOUN2) + THAT...), the "that"-modifier can actually modify either NOUN1 or NOUN2.
for instance:
the library has a new method of sorting cd's that makes certain genres of music easier to find. --> here, "that makes..." refers to the method of sorting.
the library has a new method of sorting cd's that don't fit into any of the traditional musical genres. --> here, "that don't fit..." refers to the cd's, not the method.
both sentences are correct.

however, in the example above, either of these two interpretations leads to an absurd sentence -- neither the method (= NOUN1) nor the mineral (= NOUN2) "was as early as the 18th century" -- so this option is flat-out incorrect.

(E) inappropriate tense.
if the past perfect is used to describe a state or description of something (as opposed to an action verb), it should generally be used to describe a state/description that is no longer the case. since leaching is presumably still an extraction method (this is not the sort of thing that is subject to change), the past perfect is inappropriate.

also, the modifier (starting with "well established") shouldn't be a nonessential modifier, i.e., it shouldn't be set off by commas.

1.句子结构，AB错
2.动词时态，没有必要用过去完成，E错。
3.修饰词的位置，well-established应该修饰的是Method,ABE错
4.简洁，D不如C简洁。

A 双主语
B 缺少谓语动词
C 正确
D that was无论是指代method还是mineral都使得后面的as early as变成从句的成分，那就变成了method（或者mineral）was as early as the eighteenth century，显然说不通。
E 时态不对，过去完成时表示leaching是过去的办法，现在不用了，但句中并没有表述这种意思

过去时态
误区：句中确实有完成时标志词until，但是这个是but后面的分句，与前面的句子直接加until还不一样；这里确实出现了过去时间点25年前，前面的句子也确实在25年前之前，但是这个没用过完，因为过去完成时表示leaching是过去的办法，现在不用了，但句中并没有表述这种意识；也就是but后面的句子无关leaching这个主语，基本是无关内容。如果but后面说这个方法leaching 25年前不用了，就不一样。
a well-established method > a method of mineral extraction, well established

D，that既可以修饰method也可以修饰mineral，意思上都说得通，引起指代歧义
E，过去完成时需要有过去的时间或动作做支撑，这里有did not；过去完成时表示一种状态时，通常表示以前时，而后来不再是的情况，这里没有说leaching现在不再是好的方法了，而是在说直到25前人们才发现leaching有效是因为细菌参与了这个过程。

又错选了e；
考察：
过去时态
误区：句中确实有完成时标志词until，但是这个是but后面的分句，与前面的句子直接加until还不一样；这里确实出现了过去时间点25年前，前面的句子也确实在25年前之前，但是这个没用过完，因为过去完成时表示leaching是过去的办法，现在不用了，但句中并没有表述这种意识；也就是but后面的句子无关leaching这个主语，基本是无关内容。如果but后面说这个方法leaching 25年前不用了，就不一样。
a well-established method > a method of mineral extraction, well established

C中as early as the eighteenth century作为状语，表示（早在18世纪时）leaching是方法，而D中that was as early as the eighteenth century是定语修饰method，表示leaching是（18世纪的）方法。我们一般说，早在某个时候，某物就已经是……

m

C中as early as the eighteenth century作为状语，表示（早在18世纪时）leaching是一种很完善的方法，而D中as early as the eighteenth century变成了定语修饰method，表示leaching是一种（18世纪完善建立的）方法。而后半句说，（直到25年前）工人才发现细菌在该过程中起作用。两个半句之间应该有对比转折的逻辑关系（用了but--应该是强烈转折和大对比的关系），因而从（）位置可以看出，C选项的对比更对称，即同样时间都作为状语而非定语。E中had been是过去完成时，容易让人以为和现在无关了，另外，同D（，well established)在句子中做定语，且是非限制性定语，使得well established 变成了一个不重要的成分，这样一来和后半句的对比就不再完整对称了。意思是leaching是一种方法，但是25年前工人才发现细菌起作用。---时间的一组对比就消失了。

as early as the eighteenth century 作为一个 状语修饰主句，表明什么时候成为一个方法；

①错选A...完全是读了后边忘了前边...A中的it是出现了的第二个主语啊...
②第一遍的时候错选了E...以为自己考虑到了时态问题...其实就是没有读清楚题目含义啊！！！（真要命）
③recovery ：~ (of sth/sb) 找回 重新获得 the recovery of the missing diamonds 丢失钻石的寻回
~ (from sth) 恢复正常状态 make a quick, speedy, good, slow, etc recovery (from illness)

C: as early as the eighteenth century 作为一个 状语修饰主句，表明什么时候成为一个方法；
D: as early as the eighteenth century 作为一个定语修饰方法；
显然，这个语境中as early as 作为状语更合适

C和D之间如何选？如果分不清extraction和extracting的话，可以这么看，D中的that was无论是指代method还是mineral都使得后面的as early as变成从句的成分，那就变成了method（或者mineral）was as early as the eighteenth century，显然说不通。再看C中as early as the eighteenth century是一个时间状语，很完美！

either of these two interpretations leads to an absurd sentence -- neither the method (= NOUN1) nor the mineral (= NOUN2) "was as early as the 18th century" -- so this option is flat-out incorrect. from Ron about why D is incorrect

A 两个主语
B but前面没有谓语动词
D 有时间节点用名词
E 完成时不对