请教大全上的几题？

elitist

41.According to a study published by Dr. Myrna Weissman, only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four.
(A) only one percent of Americans born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four
(B) only one percent of Americans born before 1905 suffer major depression by the age of seventy-five; if they are born since 1955, six percent become depressed by age twenty-four
(C) of Americans born before 1905, only one percent of them have suffered major depression by age seventy-five, but six percent of those born since 1955 do by the age of twenty-four
(D) major depression is suffered by the age of seventy-five by only one percent of Americans born before 1905, and by age twenty-four by the six percent born since 1955
(E) Americans born before 1905 suffer major depression by the age of seventy-five only one percent of the time, but six percent of those born since 1955 did so by age twenty-four
答案是A，C选项是时否态错了，those没有逻辑指带，but是否不对？C的those是否是指Americans born before 1905

48.According to some analysts, whatever its merits, the proposal to tax away all capital gains on short-term investments would, if enacted, have a disastrous effect on Wall Street trading and employment.
(A) its merits, the proposal to tax
(B) its merits may be, the proposal of taxing
(C) its merits as a proposal, taxing
(D) the proposal’s merits, to tax
(E) the proposal’s merits are, taxing
答案是A，B为什么不对？

50.According to some economists, the July decrease in unemployment so that it was the lowest in two years suggests that the gradual improvement in the job market is continuing.
(A) so that it was the lowest in two years
(B) so that it was the lowest two-year rate
(C) to what would be the lowest in two years
(D) to a two-year low level
(E) to the lowest level in two years
答案是E，为什么D不对？

robert

48.是proposal的用法问题，而且whatever its merits是经典的省略结构

50.lowest的意思恐怕不是two year low所能表达的巴，这完全篡改了原文的意思。

41.我也说不很清楚，c的确是时态有问题，but我觉得改变了原文的结构和意思，本来是两句并列，现在改成转折了

elitist

明白了，谢谢！！