What is true about demand curves?

Demand curves illustrate the relationship between the price of a good and the quantity demanded by consumers. The statement that they have a negative slope is true because as the price of a good decreases, the quantity demanded typically increases, and vice versa. This negative slope reflects the law of demand, which states that there is an inverse relationship between price and quantity demanded: higher prices generally discourage buyers, while lower prices encourage more purchases.

In contrast, the other options do not accurately describe demand curves. They do not represent production costs or prioritize the importance of uses for a good, nor are they required to be curved—in many cases, they can be linear. Thus, the characteristic of a negative slope captures the essence of how consumer behavior responds to price changes, which is fundamental to understanding demand in economics.