Suppose that the market for haircuts in a community is a perfectly competitive constant-cost industry and that the market is initially in long-run equilibrium. Subsequently. an increase in population increases the demand for haircuts. In the lung run, rms will the market, driving the price of haircuts and the prots of individual rms . A. enter: up; back to zero 0 8. enter, down; back to zero 0 C. leave: up; up 0 D. leave: up: back to zero