Final answer:
Perfect competition is the market structure with many firms selling identical products (c). Monopolistic competition involves many firms with similar but differentiated products. Oligopoly and monopoly represent markets with fewer firms and less product differentiation.
Step-by-step explanation:
The market structure characterized by a large number of firms selling products that appear to be identical is called perfect competition. In a perfectly competitive market, there are many firms all trying to sell homogeneous, or identical, products. Monopolistic competition involves many firms selling similar but differentiated products. These products can differ in terms of quality, design, location, and brand perception.
An oligopoly consists of only a few firms that dominate the market, which may sell identical or differentiated products. A monopoly exists when there is only one firm that controls the entire market for a product with no close substitutes.