4.b/ The fast-food industry is most likely monopolistically competitive. In a monopolistically competitive market, many firms sell products that are differentiated from one another. Each firm has a small market share and free entry and exit exist in the market. McDonald's, Wendy's, and other fast-food restaurants sell differentiated products, meaning they are not exactly alike and each has its own branding, which allows them to charge prices that are more than marginal cost. They also face competition from many other fast-food restaurants, indicating that there are many firms in the market. Therefore, the fast-food industry fits the characteristics of a monopolistically competitive market