Joint Supply Links Markets of Related Goods

Steps:

• Identify the change in X's market, such as a supply shift affecting Y's supply.
• Note that joint supply occurs when producing more X inherently produces more Y, shifting Y's supply curve rightward.
• Rule out demand-based relations like substitutes or complements, which affect demand curves.
• Confirm the diagram shows parallel supply shifts, not demand changes.

Why B is correct:

• Joint supply means goods produced together (e.g., beef and hides), so a supply increase in X causes a supply increase in Y, per the law of joint production.

Why the others are wrong:

• A: Complements shift demand for Y when X's price changes, not supply.
• C: Derived demand affects Y's demand based on X's use, not mutual supply.
• D: Substitutes shift demand for Y oppositely to X's price change.

Final answer: B