Choose the correct statement.
a. the cpi calculation assumes that everyone shops at discount stores and no one shops at convenience stores.
b. when the quality of a good improves over time, the cpi does not include the portion of the price rise attributable to the higher quality in its calculation.
c. changes in relative prices lead consumers to change the items they buy, and the cpi reflects this substitution.
d. the outlet substitution bias injects an upward bias into the cpi.