Which of the following is a requirement for dual eligibility for Medicare and Medicaid?

Dual eligibility for Medicare and Medicaid requires individuals to be enrolled in Medicare Part A and/or Part B. This enrollment is essential because it establishes eligibility for Medicare benefits, which is foundational for anyone who is also eligible for Medicaid.

Medicare Part A covers hospital insurance, while Medicare Part B covers outpatient medical services. Having coverage under these parts is a requirement because individuals who qualify for both Medicare and Medicaid (often referred to as "dual eligibles") need to have access to Medicare services to receive coordinated care across both programs effectively.

While options such as enrollment in Medicare Part D or a Medicare Advantage plan can provide additional Medicare coverage, they are not prerequisites for dual eligibility. Similarly, enrollment in a private insurance plan does not contribute to the requirements for being dually eligible, as it is separate from the federal programs of Medicare and Medicaid. Thus, the correct answer highlights the fundamental requirement that establishes access to both Medicare and Medicaid benefits.