The correct answer is: A. Perfect competition
Price discrimination is the practice of selling the same good or service at different prices to different buyers. It is possible when the seller has market power, which is the ability to raise prices without losing all of its customers.
In perfect competition, there are many sellers of a homogeneous good or service, and buyers have perfect information about prices. This means that sellers cannot charge different prices to different buyers, because buyers would simply buy from the seller who is charging the lowest price.
In monopoly, there is only one seller of a good or service. This means that the monopolist has market power and can charge different prices to different buyers. For example, the monopolist might charge a higher price to buyers who are willing to pay more, such as business customers.
In monopolistic competition, there are many sellers of a differentiated good or service. This means that each seller has some market power, but not as much as a monopolist. Sellers in monopolistic competition can charge different prices to different buyers, but they are limited by the competition from other sellers.
In oligopoly, there are a few sellers of a good or service. This means that each seller has some market power, but they are also limited by the competition from other sellers. Sellers in oligopoly can charge different prices to different buyers, but they are careful not to charge prices that are too high, or they will lose customers to other sellers.