Which of the following is a requirement for Medicare PPO enrollees?

The requirement for Medicare PPO enrollees is that they can see any doctor that accepts Medicare. This flexibility is a hallmark of Medicare Preferred Provider Organization (PPO) plans. Enrollees are not restricted to a network of providers; they have the freedom to choose healthcare providers, including specialists, without needing a referral and regardless of whether those providers are within the plan's preferred network or not.

This attribute is particularly appealing to individuals who desire a broader choice of medical providers or those who might travel frequently and require care from various physicians across different locations.

The other choices do not reflect the key features of a PPO plan. For example, requiring a primary care physician or needing referrals to see specialists is more characteristic of Health Maintenance Organization (HMO) plans, which emphasizes coordinated care through a primary doctor. Additionally, while there may be out-of-network costs associated with seeing providers outside of the network, PPOs do allow members to receive care from out-of-network providers, which is not permitted in certain plan types.