Final answer:
A shift in the demand curve is caused by a change in one of the demand determinants, not by a change in the price of the good itself. The law of demand is shown when consumers want to buy more of a good at a lower price than at a higher price, as with Sue wanting more candy bars at $1 than at $2.
Step-by-step explanation:
To answer the questions relating to demand and the law of demand, it's important to understand the concepts involved clearly. First, a shift in the demand curve is caused by: (c) a change in one of the determinants of demand. This includes factors such as changes in consumer tastes, income, price of related goods (complements or substitutes), and expectations about future prices. It does not occur because of a change in the price of the good itself, which instead causes a movement along the demand curve.
The choice that illustrates the law of demand is (d) Sue wants to buy more candy bars at $1 than at $2. This is because the law of demand states that, ceteris paribus, when the price of a good falls, the quantity demanded will increase, and vice versa. Therefore, Sue wanting to buy more at a lower price and less at a higher price exemplifies this economic principle.