求助一道之前没有讨论过的OG题~

Ashley0814

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 bv 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
虽然这个题从平行角度以及排除D,E之后就是B选项是正确答案，可是露珠还是有以下疑问，简直就是搪塞在胸！！
1，B中not just...but also有这个结构么。。。
2.我认为A中because of 后面就是接的核心名词，比B中从句简洁需要，如果A中but 之后改成与之前平行是不是就对了？
3，我实在不理解C中的are becoming这个时态。。。
希望NN和BB给解答一下，一上午就没看几道题

1327731333

表示正在， 现在也在发生

Ashley0814

1327731333 发表于 2015-11-20 23:55
表示正在， 现在也在发生

谢谢哦~
不过前两个问题可以解答吗？

1327731333

1、not but 无also
2、对

Ashley0814

1327731333 发表于 2015-11-21 14:08
1、not but 无also
2、对

蟹蟹啦~~