Explanation:

- Perfect Competition (Option 1): In this market structure, numerous firms sell identical products. Everyone is a price taker, and there is free entry and exit from the market.

- Imperfect Competition (Option 2): This is a broad term covering any market structure that doesn't meet the criteria of perfect competition. It includes monopolistic competition, oligopoly, and monopoly.

- Monopolistic Competition (Option 3): Here, many firms sell products that are similar but not identical. Firms have some degree of market power as they differentiate their products.

- Oligopoly (Option 4): A few large firms dominate this market. They may sell identical or differentiated products, and strategic interactions are crucial.