Answer:
C) earning an economic profit.
Explanation:
Since the market is in long run equilibrium, the demand = the supply of haircuts, and an increase in the quantity demanded will increase the equilibrium price in the short run, generating economic profits at least until more suppliers enter the market and long run equilibrium is established again. Economic profit doesn't exist when the market is at long run equilibrium.
*Economic profit = accounting profit - implicit costs. So economic profit being $0 in the long run doesn't mean the businesses are not making an accounting profit.