What is a defining feature of a monopoly?

A defining feature of a monopoly is the absence of competition in the market. In a monopolistic market, a single seller or producer controls the entire supply of a product or service, giving them significant market power and allowing them to set prices without concern for competitors. This lack of competition means that consumers have few, if any, alternative choices for purchasing the product, which can lead to higher prices and reduced availability of options.

The other choices highlight characteristics often found in competitive markets rather than monopolies. Low prices due to high competition indicates a market where multiple sellers are vying for consumers' business, leading to lower prices. Availability of many substitute products suggests a market rich with choices, allowing consumers to switch to different products based on preferences or price. Lastly, a variety of sellers competing equally is a hallmark of perfect competition, where multiple sellers can coexist, each having a small market share and none being able to control the market dynamics to the same extent as a monopoly does.