Explanation:

- Option 1: Preventive medicine

- This refers to actions taken to prevent diseases rather than curing them. It includes immunizations and health education.

- Option 2: Curative medicine

- This involves treatments and medical interventions aimed at curing illnesses or medical conditions.

- Option 3: Social medicine

- This examines how socio-economic factors affect health, including public health policies and community-based health care.

- Option 4: All of the above

- Expenditure on health, in the context of human capital formation, encompasses all these areas. They all contribute to enhancing a population's health and productivity.