If the price of apple pies rose to $100 per pie, consumers would purchase fewer pies than if the price were $5 per pie. If the price of ice cream fell to $0.30 per scoop, consumers would purchase more ice cream than if the price were $5 per scoop. These relationships illustrate the:
a. Law of demand
b. Law of supply
c. Difference between normal and inferior goods
d. Difference between substitute and complement goods