Explanation:

- Monopoly (Option 2): In a monopoly, one firm controls the market, allowing it to set different prices for different consumers. This is because there are no close substitutes and minimal competition, which gives a monopoly the power to engage in price discrimination.

- Monopolistic Competition (Option 1): In this market structure, many firms sell similar but not identical products. While firms have some pricing power, the existence of substitutes and competition limits the extent of price discrimination.

- Perfect Competition (Option 3): Firms sell identical products, and no single firm can influence the market price. Thus, price discrimination is not possible here.

- Oligopoly (Option 4): Few firms dominate the market, and price discrimination can occur, but it’s less prevalent than in monopolies because of competitive factors and strategic pricing between firms.