A monopoly exists when:

A monopoly exists when one company controls an entire product market unfairly. This situation typically arises when a single business has such a dominant position that it can dictate terms, control prices, and limit competition, often leading to a lack of choices for consumers. Monopolies can stifle innovation and lead to higher prices since consumers have no alternative providers for the product or service in question.

In a monopolistic market, the absence of competitors allows the monopolist to operate without the pressures that would otherwise come from other businesses striving for market share. This can result in inefficiencies and a decline in the overall quality of goods or services. Thus, the defining characteristic of a monopoly is its control and the lack of fair competition, making the answer about one company unfairly controlling an entire product market the correct choice.