请教大全天山真题12,18,20

lingxia

12.    Lincoln, discovering in young manhood the secret that the Yankee peddler has learned before him, knew how to use a good story to generate good will.
(A) Lincoln, discovering in young manhood the secret that the Yankee peddler has learned before him, knew
(B) Discovering in young manhood the secret that the Yankee peddler has learned before him, Lincoln knew
(C) Lincoln, discovering the secret that the Yankee peddler had learned in young manhood before him, knew
(D) In young manhood Lincoln discovered the secret that the Yankee peddler had learned before him;
(E) Lincoln, discovered in young manhood the secret that the Yankee peddler had learned before him, knew
答案为B，为什么has learned 为正确的时态，而C中的had learned 不对呢？
主句时态为knew，从句中为什么用has learned？

18.    Interest rates on mortgages have declined steadily during the first six months of this year but virtually remained unchanged during the next three months.
(A) have declined steadily during the first six months of this year but virtually remained unchanged
(B) declined steadily during the first six months of this year but virtually remain unchanged
(C) steadily declined during the first six months of this year but remain virtually unchanged
(D) declined steadily during the first six months of this but have remained virtually unchanging’
(E) declined steadily during the first six months of this year but have remained virtually unchanged
答案为E，A为什么不对呢？两个都用完成时态不可以吗？
Have declined……….but (have) virtually remained………

20.    uritan fanatics brought to civil and military affairs a coolness of judgment and mutability of purpose that some writers have though inconsistent with their religious zeal, but which was in fact a natural outgrowth of it.
(A) but which was in fact a natural outgrowth of it
(B) but which were in fact a natural outgrowth of it
(C) but which were in fact natural outgrowths of it
(D) but it was in fact a natural outgrowth of them
(E) which was in fact a natural outgrowth of it
though是否为打错，应为thought吧？
That 从句修饰的对象是否是judgment and mutability of purpose ？but which的修饰对象应该和that修饰的一样吧，后面的it指代什么呢？
这句话怎么理解？

rt316

1-我觉得时态好像的确不对。C错在in结构的修饰对象发生变化，改变句义。
2-现在完成时态通常表示动作延续至今，但是从句义上很明显看出，前面的动作是发生在至少3个月前的，所以，前半句应该用一般过去时。
3-我觉得but好像是多余的，因为从平行结构来看，but后的which没有对应结构，it觉得应该指代purpose，即：宗教的热情来自于目的（或意志）。bring to B A是bring A to B的倒装结构。thought应该是对的。

顺便说一句，如果方便的话，请告诉我你这些题的出处。我想稍微研究一下，因为我觉得不太象真题，而且有打印错误。或许是我认识上的不足。不过，在语法题上，若是题目的打印错误比较多的话，建议大家还是放弃这类题目比较好。
拙见。

lingxia

谢谢！

这些题目是从CD上当下来的，就在12月4日更新的GMAT SC大全.doc里

能否再看看我贴的4、7、8