Final answer:
The assertion that Part D of Medicare covers prescription drug services is true, as established by the Medicare Prescription Drug, Improvement, and Modernization Act of 2003.
Step-by-step explanation:
It is indeed true that Part D of Medicare covers prescription drug services. After identifying the need for such coverage, particularly for the elderly and disabled who often require several prescription drugs, the Medicare Prescription Drug, Improvement, and Modernization Act was signed into law in 2003. This act includes measures to help with prescription drug costs, such as a prescription drug benefit where individuals pay an annual premium and deductible. In return, the federal government covers 75% of their prescription drug costs up to a certain limit. Medicare Part B, on the other hand, is an optional program that covers physician services, medical tests, and outpatient visits but not prescription drugs.