Consider a U-shaped long-run average cost curve that has a minimum efficient scale at 6,000 units of output. In this case, this industry would be

A) perfectly competitive if the market quantity demanded is 20,000 units.
B) monopolistically competitive if the market quantity demanded is 12,000 units.
C) an oligopoly if the market quantity demanded is 18,000 units.
D) an oligopoly if the four-firm concentration ratio is more than 10 percent.

Answer: C