What characterizes a monopoly in market structure?

A monopoly in market structure is characterized by a single seller controlling the entire market for a particular good or service. This unique position allows the monopolist to set prices without competition, as there are no direct alternatives available to consumers. The lack of competition means that the seller has significant market power and can influence supply levels and pricing strategies, which can lead to higher prices for consumers compared to markets with more competition. A monopoly often arises due to barriers to entry that prevent other firms from entering the market, such as high startup costs, exclusive access to resources, or strong brand loyalty.

The other options do not correctly describe a monopoly. For instance, having a few sellers dominating the market describes an oligopoly, while a market with multiple close substitutes indicates a competitive market structure. Lastly, monopolies can be subject to government regulation, which can limit their pricing power and protect consumer interests, making the absence of regulation not a defining feature of a monopoly.