The correct answer is: D. Perfect competition
In perfect competition, there are many firms selling identical products, and no one firm has a significant share of the market. This means that firms have no control over the price of their product, as they must charge the same price as all the other firms in the market.
A monopoly is a market structure in which there is only one firm selling a good or service. This firm has a great deal of market power and can therefore charge a higher price for its product.
Monopolistic competition is a market structure in which there are many firms selling similar but not identical products. Firms in a monopolistically competitive market have some control over the price of their product, but they are not able to charge as high a price as a monopoly firm.
An oligopoly is a market structure in which there are a few large firms selling a good or service. These firms have a great deal of market power and can therefore charge a higher price for their product.
In conclusion, the correct answer is D. Perfect competition.