GWD-5-Q39

In 2000, a mere two dozen products accounted for half the increase in spending on prescription drugs, a phenomenon that is explained not just because of more expensive drugs but by the fact that doctors are writing many more prescriptions for higher-cost drugs.

A. a phenomenon that is explained not just because of more expensive drugs but by the fact  that doctors are writing
B. a phenomenon that is explained not just by the fact that drugs are becoming more expensive but also by the fact that doctors are writing
C. a phenomenon occurring not just because of drugs that are becoming more expensive but because of doctors having also written
D. which occurred  not just because drugs are becoming more expensive but doctors are also writing
E. which occurred not just because of more expensive drugs but because doctors have also written
GWD上的电影：B  

我觉得B的时态不对...the fact that也是不简洁的结构...

其他几项的错误大家帮我看看我的看法是否有误：

A. explain和because的重复。 not just...but...后面内容不平行。时态也有问题...

B. 明显的时态不对，应该用过去时（因为解释的是2000的事情）...the fact that也是不简洁的结构...

C. 独立主格是可以的，伴随原因。 doctors后面少了个所有格符号。只是are becoming的时态也觉得不妥...

D. not just...but...后面内容不平行。which指代错误

E. which指代错误。have written是属于现在完成时，我觉得应该用过去完成时...且not just...but...形式上不平行

n+having done是绝对错误的；because of把整体概念变成部分概念；but also 中间不能加成分

关于时态：

现在进行时有表示习惯进行：表示长期的或重复性的动作，说话时动作未必正在进行。

　　Mr. Green is writing another novel.

　　(说话时并未在写，只处于写作的状态。)

　　She is learning piano under Mr. Smith.

我想这里drugs are becoming more expensive but also by the fact that doctors are writing的药更贵，医生往贵药开也是从2000年以来的一种长期动作，处于这种状态

另外，从accounted看出，2000已经过去，a phenomenon that is explained 中的is看出这种现象可以通过一种一直长期存在的状态来解释