8. As firms enter a monopolistically competitive industry, each firm's share of the market increases _____ 19. As firms enter a monopolistically competitive industry, each firm must increase advertising costs in order to maintain their share of the market _____ 20. As firms exit a monopolistically competitive industry, each firm's share of the market increases _____ 21. Monopolistic competitors have no incentive to advertise because they can sell any amount at the market price _____ 22. Monopolistic competitors must advert