Concept:A downward sloping demand curve shows the inverse relationship between price and quantity demanded.Explanation:According to the law of demand, when the price of a commodity falls, its quantity demanded rises.Consumers are willing to buy more only at a lower price.This is because a lower price increases real income and makes the good more attractive compared to substitutes.Therefore, to sell a larger quantity, the seller must reduce the price.Answer:Option D: price must be lowered to sell more.