Final answer:
Mr. Clifford's downward-sloping demand curve illustrates the law of demand, which states that higher prices lead to lower quantity demanded, and lower prices increase demand. The correct option is d.
Step-by-step explanation:
When Mr. Clifford shows a downward-sloping demand curve, he is illustrating the law of demand. This economic principle posits that, all else being equal, as the price of a product increases, the quantity demanded decreases.
Conversely, as the price decreases, the quantity demanded increases. This relationship is represented graphically by a demand curve that slopes downward from left to right.
Demand curves can look different for various products, being steep or flat, straight or curved, but they typically share this downward slope. The correct option is d.