Final answer:
Under an HMO plan, prescription drugs, preventive services, and mental health care are considered supplemental benefits, but long-term care is not typically covered.
Step-by-step explanation:
The supplemental benefits under an HMO plan typically include prescription drugs, preventive services, and mental health care. These are meant to provide comprehensive care to the insured individuals. However, HMO plans do not typically cover long-term care, as this kind of care usually entails ongoing assistance with basic personal tasks of everyday life, possibly extending over several years. HMO plans are designed to provide medical care and are funded to handle costs associated with shorter-term health interventions rather than long-term care scenarios.