Infrastructure generally refers to the fundamental facilities and systems serving a country, city, or area, including the services and facilities necessary for its economy to function. Based on this definition, the best option that exemplifies infrastructure among the choices provided would be:
D: oil refinement and health care
Both oil refinement and health care are critical components of infrastructure, as they relate to essential services that support societal function and economic activity.
Choices A (crops), B (politicians), and C (institutions, administration, and education) do not fit the typical definition of infrastructure as closely as option D does.