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 答案是B，很想知道B中的but also 不是必须要和not only对应么？难道和not just也可以么？