Answer:
A. The D-curve shifts to the right
Step-by-step explanation:
Nike and Reebok are supplement goods. It means customers can use either of two brands of shoes with almost equal satisfaction. A change of preferences by customers will influence the demand for supplement goods.
If Nike becomes unpopular, the demand for Reebok will increase. Because the increase in demand is not due to price changes, the demand curve will shift to the right. A shift in the demand curve means that the quantity demanded increases at all prices.