Perfectly competitive markets are economically efficient in the long run, partly because Select one: a. entry barriers enable such firms to invest in high-return capital projects. b. firms in these industries produce an output where the price is equal to the minimum average variable cost. c. the price consumers are willing to pay for the last unit just equals the cost of having to produce that additional unit. d. entry and exit guarantees a positive long-run profit above average total cost for each firm.