Final answer:
Other market structures are considered 'imperfect' because they may not achieve either productive or allocative efficiency (option c). Productive efficiency occurs at the lowest cost, and allocative efficiency matches the price to the marginal cost, both of which are not consistently found in imperfect markets.
Step-by-step explanation:
Productive efficiency and allocative efficiency are two concepts achieved in the long run in a perfectly competitive market. These efficiencies are why this type of market is considered 'perfect'. In contrast, when analyzing other market structures, they are often la beled 'imperfect' due to not achieving these efficiencies.
Productive efficiency occurs when goods are produced at the lowest possible cost, which typically happens when firms operate at the bottom of their average total cost curves. Allocative efficiency occurs when the price of the good is equal to the marginal cost of production, ensuring that resources are distributed to their most valued use and providing maximum satisfaction to society.
Therefore, the correct option to describe why other market structures are 'imperfect' is: c. Imperfect markets may not achieve either productive or allocative efficiency. This is the case because such markets can have barriers to entry, market power, or other distortions that prevent firms from operating at minimum cost or producing the quantity where price equals marginal cost.