Joint Demand as Complementary Goods

Steps:

• Identify joint demand: Products consumed together, increasing demand for each other.
• Review choices: Look for items that pair directly with a smartphone for use.
• Eliminate substitutes or unrelated items: Focus on complements, not alternatives or inputs.
• Select the best match: Choose the accessory that enhances smartphone functionality.

Why C is correct:

• Headphones are complementary goods in joint demand with smartphones, as defined in economics: their demand rises together because they are used jointly for audio features like calls or music.

Why the others are wrong:

• A: Alternative smartphone is a substitute, competing in demand rather than joint.
• B: PC is unrelated; it doesn't complement smartphone use directly.
• D: Metals are production inputs, creating derived demand, not joint consumption.

Final answer: C