The substitution effect is the change in the quantity demanded of a good that results from ______________, holding constant the effect of the price change on consumer purchasing power.
a. the tendency of people to be unwilling to sell something they own
b. a change in price making the good more or less expensive relative to other goods
c. a change in the price of a substitute for the good
d. an increase in the usefulness of a product as the number of consumers who use it increases