The demand curve is a graphic representation of:

a. the relationship between price and quantity supplied of a certain good or service.
b. the relationship between price and quantity demanded of a certain good or service.
c. the relationship between supply and demand for a certain good or service.
d. the relationship between productivity and quantity demanded of a certain good or service.

b. the relationship between price and quantity demanded of a certain good or service.

The demand curve is a graphic representation of the relationship between price and quantity demanded of a certain good or service.