Explanation:

- Monopoly:

- Correct Answer: Monopolies often practice price discrimination because they have significant control over the market. They can charge different prices to different consumers based on their willingness to pay.

- Monopolistic Competition:

- Firms have some ability to price discriminate due to product differentiation. However, the degree is less compared to monopolies.

- Perfect Competition:

- No price discrimination is possible. All firms sell identical products, and prices are determined by supply and demand.

- Oligopoly:

- Some price discrimination can occur if firms have market power and can segment the market.