"Free" means available at no cost

Steps:

• Define "free" as something obtained without payment or exchange.
• Assess each option for inherent costs or funding sources.
• Eliminate options involving production, taxes, or purchase.
• Identify the naturally occurring, costless element.

Why D is correct:

• Sunlight is a natural resource provided by the sun with zero cost, per the economic definition of "free goods" as unlimited and unpriced.

Why the others are wrong:

• A: Free samples incur production and distribution costs to the provider.
• B: State health services are funded by taxpayer money, not truly free.
• C: Second-hand clothing requires payment to acquire from sellers.

Final answer: D