The correct answer is: C. 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 would be possible in a competitive market, because consumers have no other choice but to buy from the monopolist.
Imperfect competition is a market structure in which there are a few large firms that sell a similar product. These firms have some control over the price of their product, but not as much control as a monopolist. This is because consumers have some choice between the different firms, so the firms cannot charge a price that is too high.
Perfect competition is a market structure in which there are many small firms that sell an identical product. These firms have no control over the price of their product, because consumers will simply buy from the firm that charges the lowest price.
In conclusion, the degree of control over the price of its product by a firm is very large in a monopoly market structure.