The CPI overestimates changes in the cost of living because

a. the growth of discount stores where consumers can obtain goods at discount prices has not been adequately represented in the construction of the CPI.

b. the CPI does not adequately deal with changes in the quality of products over time.

c. the CPI deals with a fixed market basket and doesn’t capture the savings households enjoy when they substitute cheaper alternatives in response to a price change.

d. of all of the above.