A demand curve or a demand schedule for a good or service is a plot on the quantity-price (QP) plane. A demand schedule is a table showing how much of a given product an individual or a household would be willing to buy at different prices. Demand curves are usually derived from the given information of demand schedules. On a demand schedule, there is information about the price and quantities demanded at each different price. The quantity demanded is the amount of a good that an individual or a household would buy in a given time period at the current market price.

It maps alternative price levels to different quantities that an individual or a group of individuals are willing and able to buy at each of those price levels, when income level and other factors affecting demand are held constant. In other words, a demand curve shows how much more of a product an individual is willing to buy when its price falls in the absence of a change in that individual’s income, tastes, etc. As it is understood from the information given the price of the good isn’t held constant, so the correct answer is “D”.