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.

• Aa phenomenon that is explained not just because of more expensive drugs but by the fact that doctors are writing  
• Ba phenomenon that is explained not just by the fact that drugs are becoming more expensive but also by the fact that doctors are writing  
• Ca phenomenon occurring not just because of drugs that are becoming more expensive but because of doctors having also written  
• Dwhich occurred not just because drugs are becoming more expensive but doctors are also writing  
• Ewhich occurred not just because of more expensive drugs but because doctors have also written