Health Maintenance Organizations (HMOs) in Virginia, per Virginia Code § 38.2-4306, emphasize preventive care to reduce long-term costs. Preventive services, as defined in the study guide and aligned with ACA standards, include childhood immunizations (option C), such as vaccines for measles or polio, offered at no cost to members. Option A (rehabilitation therapy) is restorative, not preventive, addressing existing conditions. Option B (treatment for alcoholism) is a treatment service, not prevention, though HMOs cover it separately. Option D (home health services) supports recovery or chronic care, not primary prevention. The study guide likely lists immunizations as a core preventive benefit, contrasting them with treatment-oriented services, confirming C as the correct answer.