What enrollment requirement does Mrs. Mulcahy have to meet to enroll in a Medicare prescription drug plan?

To enroll in a Medicare prescription drug plan, Mrs. Mulcahy must meet the requirement of being entitled to Part A. This entitlement signifies that she is eligible for Medicare hospital insurance, which is a key component of the Medicare system. While enrollment in Part B is also beneficial for comprehensive coverage, the primary criterion for eligibility to join a Medicare prescription drug plan is the entitlement to Part A.

Being entitled to Part A means that she has met the necessary criteria, such as age (at least 65) or qualifying disability status, which are fundamental to accessing Medicare benefits. This entitlement provides a baseline eligibility that supports enrollment in additional services, including prescription drug coverage.

Although having Part B would generally enhance her coverage and options, it is not strictly required for eligibility to enroll in a Medicare prescription drug plan. Therefore, the correct answer emphasizes the necessity of entitlement to Part A as a foundational requirement for participation in the Medicare prescription drug program.