Which of the following best describes demand? Select one: O a. A change in quantity demanded is a movement along the demand curve, and a change in demand is a shift in the demand curve. O b. A change in demand is a movement along the demand curve, and a change in quantity demanded is a shift in the demand curve. O c. Both a change in quantity demanded and a change in demand are shifts in the demand curve, only in different directions. O d. Both a change in quantity demanded and a change in demand are movements along the demand curve, only in different directions