What involves firms competing against the same rivals in multiple markets?

Multimarket competition refers to the scenario where firms compete against the same rivals in more than one market. This type of competition can significantly impact strategy and market behavior, as firms must consider the interconnectedness of different markets and the competitive dynamics present in each.

When firms are involved in multimarket competition, they often engage in strategic maneuvers that can include price setting, marketing strategies, and product development tailored to their rivals' actions not just in a single market, but across several markets. This can create a situation where firms may avoid aggressive competition in one market to preserve their relationship or competitive stance in another, leading to a more complex and interdependent relationship among competitors.

The other types of competition mentioned—monopolistic, oligopolistic, and duopoly—refer to different competitive structures that do not necessarily encompass the concept of competing in multiple markets simultaneously against the same rivals. Monopolistic competition typically involves many firms competing in a single market with differentiated products, while oligopolistic competition suggests a market dominated by a few large firms, and duopoly refers specifically to competition between two firms in a single market. Therefore, multimarket competition is the most accurate answer for the scenario described.