To be eligible for a stand-alone Part D plan, what must an enrollee be entitled to?

To be eligible for a stand-alone Part D plan, an individual must be entitled to either Medicare Part A or enrolled in Medicare Part B, in addition to residing in the drug plan's service area. This eligibility criterion ensures that individuals who are either eligible for hospital insurance through Part A or outpatient insurance through Part B can access prescription drug coverage that complements their existing Medicare benefits.

Part A covers inpatient hospital stays, skilled nursing facility care, hospice care, and some home health care, while Part B covers outpatient services, including doctor visits and preventive care. Therefore, the requirement of being entitled to either one of these parts ensures that potential enrollees have some level of Medicare coverage, which is essential for Part D enrollment.

Residing in the plan's service area is also crucial, as Part D plans are geographically limited and provide coverage only to those within their specified regions. This ensures that enrollees have access to local pharmacies and can effectively utilize their benefits.

The other options do not encompass the necessary conditions for eligibility, such as requiring both Part A and Part B or only being enrolled in one part, which overlooks the flexibility provided by the eligibility criteria.