5. Chapter ma2pe09r, Section .16, Problem 014 (ID: 014.16.MANK09) When an industry has many firms, the industry is Oa. an oligopoly if the firms sell differentiated products, but it is monopolistically competitive if the firms sell identical products. Ob. monopolistically competitive if the firms sell differentiated products, but it is perfectly competitive if the firms sell identical products. Oc. perfectly competitive if the firms sell differentiated products, but it is monopolistically competitive if the firms sell identical products. Od. an oligopoly if the firms sell differentiated products, but it is perfectly competitive if the firms sell identical products