Free goods are unlimited natural resources available without production cost or scarcity.

Steps:

• Define free good as a resource abundant in nature, not scarce, and requiring no human effort to obtain.
• Assess each option for scarcity and cost: defence, education, and health services involve production and payment; sunshine does not.
• Eliminate options needing resources or labor, leaving natural phenomena.
• Confirm sunshine fits as it's freely available from the sun without limits or cost.

Why D is correct:

• Sunshine is a classic free good per economic definition, as it's naturally unlimited and accessible without production or rivalry.

Why the others are wrong:

• A: Defence is a public good provided by governments, involving costs and scarcity of resources.
• B: Education requires teachers, facilities, and funding, making it scarce and costly.
• C: Health services demand medical expertise and infrastructure, leading to high costs and limited supply.

Final answer: D