The correct answer is: B. Monopoly
A monopoly is a market structure in which there is only one seller of a good or service. The demand curve for a monopoly firm is the market demand curve, which is downward-sloping. This means that the firm can charge a higher price and still sell some units of its product.
In perfect competition, there are many sellers of a good or service, and the demand curve for each firm is perfectly elastic. This means that the firm can only charge the market price, and if it charges any higher, it will sell no units of its product.
In an oligopoly, there are a few sellers of a good or service, and the demand curve for each firm is downward-sloping but not as steep as the demand curve for a monopoly firm. This means that the firms in an oligopoly have some market power, but they are not able to charge as high a price as a monopoly firm.
Bicameralism is a system of government in which there are two legislative chambers. This is not a market structure.