The correct answer is A. Monopoly.
A monopoly is a market structure in which there is only one seller of a good or service. This means that the monopolist has a great deal of control over the price of its product. The monopolist can charge a higher price than it would if there were other sellers in the market, because consumers have no other choice but to buy from the monopolist.
An imperfect competition is a market structure in which there are a few large sellers of a good or service. These sellers have some control over the price of their product, but not as much as a monopolist. This is because consumers have some choice about which seller to buy from.
An oligopoly is a market structure in which there are a few large sellers of a good or service. These sellers have a great deal of control over the price of their product, because consumers have little choice about which seller to buy from.
Perfect competition is a market structure in which there are many small sellers of a good or service. These sellers have no control over the price of their product, because consumers have a great deal of choice about which seller to buy from.
In conclusion, the correct answer is A. Monopoly.