Which of the following is a common resource?

• A. Fisheries
• B. National defense
• C. Clean water treated as a public good
• D. Private membership parking

Answer: (A)

A common resource is something non-excludable but rival in consumption: many people can use it, but one person’s use reduces the amount available for others. Fisheries fit this pattern because the ocean’s fish are accessible to many fishers, and catching fish lowers the stock for everyone else. This open-access nature can lead to overuse and depletion unless rules limit harvests, licenses, or quotas. National defense, by contrast, is a public good—non-excludable and non-rival—so one person’s protection doesn’t diminish another’s. Private membership parking is a private good—excludable and rival. Treating water as a public good would imply non-excludable and non-rival benefits, which isn’t the usual case for a finite water supply, so it’s not a classic common resource.