时态啊时态！（三道题，乱了乱了）

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

B其他地方没有问题，可是为什么用has不用had呢？

    During the Renaissance, scholars were uncertain as to the location of Troy, and by the eighteenth century many historians doubted that Troy had ever existed.(A)

另外还有by+点时间修饰的动作一般来说用完成时，但是这道题却用了一般过去时……无语了。

      Where once the union had acquiesced to the prejudices of its English-speaking members by supporting the imposition of an alien tax on immigrant workers,  the United Mine Workers made a determined effort to enlist Italians and Slavs in its ranks.（A）

最恐怖的是，once这个词我一直无法理解，虽然这道题可以从after 1897推断出来前面的用过去完成时，但是once不是表示一般过去的点时间的么？

救命了啦~~~~

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）

(E) declined steadily during the first six months of this year but have remained virtually unchanged

虽然每道题的时态都要视情况而定，但是这道题同样是during,为什么E后面非要用完成时？我觉得用一般现在时也不是绝对的错误，毕竟during the next three months没有明说“一直到现在”或者“对现在的影响”呀……为什么为什么……谁能帮忙总结一下……

1. 关于Lincoln那题，我觉得用has的确讲不通，怀疑题错了。

2.During the Renaissance, scholars were uncertain as to the location of Troy, and by the eighteenth century many historians doubted that Troy had ever existed.

3.Where once the union had acquiesced to the prejudices of its English-speaking members by supporting the imposition of an alien tax on immigrant workers, after 1897 the United Mine Workers made a determined effort to enlist Italians and Slavs in its ranks.

(A) Where once the union had acquiesced to the prejudices of its English-speaking members by supporting

(B) Where once the union acquiesced to it English-speaking members’ prejudice for the support of

(C) While once the union had acquiesced to the prejudices of its English-speaking members in support of

(D) While once the union acquiesced to its English-speaking members’ prejudice in supporting

(E) While once the union had acquiesced to the prejudices of its English-speaking members in its supporting of

（1）.AB相比：B中it English-speaking members’ prejudice不对，A更好；

（2）.CDE比：3句意思接近，D中support为动词，CE中support为名词，D更好。

（3）.AD再比：A表示the union用support imposition的方式来acquiesced prejudice,意思更讲的通。