Answer:
1. Economics - The social science concerned with how individuals, institutions, and society make optimal (best) choices under conditions of scarcity.
2. Opportunity cost - The next-best thing that must be forgone in order to produce one more unit of a given product.
3. Marginal analysis - Making choices based on comparing marginal benefits with marginal costs.
4. Utility - The pleasure, happiness, or satisfaction obtained from consuming a good or service.