Final answer:
The market structure with 'no close substitutes' is a monopoly, as it includes a single firm with significant market power and the lack of competition.
Step-by-step explanation:
The market structure that possesses the characteristic "no close substitutes" is monopoly. In a monopolistic market, one firm produces all of the output in the market, facing no significant competition. Consequently, they can set prices with considerable market power. In a monopoly, there is only one firm in the market, which means there are no competitors offering similar products or services.
This gives the monopolistic firm the ability to set prices without worrying about price competition. By contrast, perfect competition features a large number of firms dealing in identical products, and monopolistic competition features many firms that engage in product differentiation but still face competition. Neither of these conditions aligns with the concept of having no close substitutes, which is unique to a monopoly.