Public Goods Require Non-Rivalry

Steps:

• Define public good as a resource where consumption by one does not diminish availability for others and exclusion is impossible.
• Examine choices against economic definition from Samuelson: goods jointly consumed without rivalry or excludability.
• Eliminate options not central to the core traits.
• Confirm non-rivalrous as essential for free-rider problems and market failure.

Why C is correct:

• Non-rivalrous means one person's use does not reduce benefits for others, per Samuelson's public goods definition, enabling simultaneous consumption.

Why the others are wrong:

• A: Opportunity cost exists for all scarce resources, including public goods like national defense.
• B: Non-excludable is necessary but not sufficient alone; club goods are excludable yet non-rivalrous.
• D: Essentiality relates to needs, not economic classification of public goods.

Final answer: C