Final answer:
When the American Heart Association declares that peaches promote good heart health, it is likely to increase demand (D) for peaches. Therefore, the correct answer is Quantity demanded (Qd) decreases.
Step-by-step explanation:
When the American Heart Association declares that peaches promote good heart health, it is likely to increase demand (D) for peaches. As a result, the demand curve for peaches will shift to the right, from the original position (Do) to a new position (D₁). This means that at every given price, the quantity demanded (Qd) of peaches will be higher compared to before.
Therefore, the correct answer is d) Quantity demanded (Qd) decreases.