Final answer:
Tje correct answer is option c. The only seller in a market is correctly defined as a monopolist pure. Differentiating from oligopolists and cartels, the monopolist holds exclusive control over the market without competition. The right answer to the given multiple choice question is 'monopolist pure' (option c).
Step-by-step explanation:
A monopolist is the only seller in a market, having the exclusive control over a product or service. This situation allows the monopolist to significantly influence or determine the terms on which other individuals have access to the goods and services in question.
In the context of market structures, such as those described where a few firms dominate the market, it's crucial to distinguish between different market players like oligopolists, who are part of a market structure where a few firms have substantial market power, and monopolists, who singularly possess complete market control.
In cases where firms in an oligopoly act together to reduce output and raise prices, they may form a cartel. However, this form of collusion is often illegal and unsustainable in the long term due to incentives for individual firms to cheat by expanding output. On the contrary, a monopolist pure does not share market power with competitors and is characterized by an absence of rivalry within its market space.
Therefore, when referring to the only seller in a market, the correct choice is monopolist pure (option c), who operates without competition in their segment, quite distinct from a duopolist, cartel, or oligopolist.