OG13 86时态问题

gjrichard

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

此题开头就是In 2000，那为啥不用过去式而用一般现在时呢?

448258130

后面是同位语，可以和主句时态不一样