Which of the following goods is both rival and excludable?

• A. National defense
• B. A public park that is open to everyone
• C. A broadcast television signal
• D. A slice of pizza sold at a restaurant

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the definitions of rival and excludable goods. A good is **rival** if one person's consumption of it reduces the amount available for others. A good is **excludable** if it is possible to prevent people who do not pay for it from consuming it.
2. Step 2: Analyze each option based on these definitions. For example, national defense is **non-rival** (one person's protection does not reduce protection for others) and **non-excludable** (everyone benefits regardless of payment).
3. Step 3: Consider a public park open to everyone. It is generally **non-excludable** because anyone can enter, but it can be **rival** if overcrowding reduces enjoyment or space for others.
4. Step 4: Evaluate a broadcast television signal. It is **non-rival** because one person watching does not reduce availability for others, but it can be **excludable** if access is controlled (e.g., subscription).
5. Step 5: Finally, examine a slice of pizza sold at a restaurant. It is **rival** because once eaten, it cannot be consumed by others, and **excludable** because the restaurant can prevent non-paying customers from eating it. This matches the criteria for a good that is both rival and excludable.