Final answer:
The characteristic that is not a characteristic of a perfectly competitive market structure is barriers to entry.
Step-by-step explanation:
The characteristic that is not a characteristic of a perfectly competitive market structure is C. Barriers to entry.
In a perfectly competitive market structure, there are numerous buyers and sellers, and they offer homogeneous products. Both sellers and buyers have perfect information about the products, and there are no barriers to entry, meaning firms can freely enter and exit the market.
However, in a monopolistic market structure, there are barriers to entry that prevent potential competitors from entering the market. Examples of barriers to entry include legal, technological, or market forces, such as the cost of retail space or limited radio frequencies.