Joni owns a donut shop and a car wash. The donut shop is monopolistically competitive and the car wash is perfectly competitive. Both firms make zero economic profit. What can be inferred about both firms? Select one: a. Their industries are in equilibrium; no firms will want to enter or exit. b. Other firms who wish to differentiate their product more will want to enter the market. c. Other firms who do not differentiate their product sufficiently will want to leave the market. d. Market demand shifts to the right