The demand curve illustrates the law of demand, which states that:

a) Other things equal, the quantity demanded of a good falls when the price of the good rises.
b) Other things equal, the quantity demanded of a good rises when the price of the good rises.
c) Other things equal, the quantity demanded of a good rises when the price of the good falls.
d) Other things equal, the quantity demanded of a good remains constant regardless of price changes.