Final answer:
The market structure described, with many sellers and product differentiation, is known as monopolistic competition. The correct answer is option c.
Step-by-step explanation:
A market structure characterized by many sellers with each having some pricing power and product differentiation is best described as monopolistic competition. In a monopolistic competition market, many firms sell differentiated products, which mean products are similar but varied, and there are few barriers to entry for new firms. This contrasts with an oligopoly, where a few firms dominate the market with high barriers to entry, and perfect competition, where many sellers sell identical products with no pricing power.