Which economic condition is best described by a monopoly?

A monopoly is characterized by a single entity serving as the sole provider of a particular good or service in a market. This means there is one seller, or producer, that controls the entire supply of that good or service, and as a result, it has significant power over pricing and production without facing competition.

In this context, option B accurately captures the essence of a monopoly as it specifies one seller serving multiple buyers. This highlights the lack of direct competition in the market, where consumers have no alternative suppliers. In contrast, the other options suggest scenarios with multiple sellers or buyers, which align more closely with different market structures like perfect competition or oligopoly, rather than a monopoly.