Public Goods Are Non-Excludable and Non-Rivalrous

Steps:

• Define public good: A good that is non-excludable (no one can be prevented from using it) and non-rivalrous (one person's use doesn't reduce availability for others).
• Evaluate each option against this definition.
• Identify which option fits both criteria perfectly.
• Confirm by ruling out options that fail one or both criteria.

Why A is correct:

• National defense protects all citizens simultaneously without exclusion or rivalry, matching the classic definition of a public good.

Why the others are wrong:

• B: Hospital services are excludable (patients can be denied access) and rivalrous (resources like beds are limited).
• C: Leisure center services are excludable (membership or fees required) and rivalrous (space and facilities can be overcrowded).
• D: Toll road services are excludable (tolls prevent non-payers) and rivalrous during congestion.

Final answer: A