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
题目分析：用phenomenon显然比用which更精确，干掉D和E。前三个选项无非就是not but引导的一个并列，A中not后面用because of 而but后面用by the fact显然不合适，B和C强调的语义重点不一样，B强调两个事实，而C强调药物和医生这两个主体，根据意思我们知道产生这个现象的应该是医生开药这个事实而不是医生本身，选B
