求教~大全41~

端木瑶

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

解释中说b时态错误，可是研究study这种东西难道不能用现在时态么?

they 指代不清 是不是 和 a of b 这样的问题类似哈，就是they，it 不能指代b这样子哈？

伤不起啊~谢谢了~
(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

weixun1990

感觉study陈述的是过去的事实，而且有1905年作为界限，应该用过去完成时吧；前后结构最好对称，不然不知道they是指代a of b整个还是只是b。
我也同求教，不是很确定。

lonelyorchid

B的句子明显不知道在说什么呀。什么叫做if they are born，if后面只能虚拟语气（除非条件状语。。。）
B错得一塌糊涂。。。

nichoolas

请问：语法大全有解释吗？我下的那个版本为什么没有解释- -||