When Setting Rates That Natural Monopolists Can Charge,regulatory Commissions Attempt

When setting rates that natural monopolists can charge,regulatory commissions attempt to establish a maximum price:

A) at the minimum long-run average cost of the monopolist.
B) at the minimum short-run average cost of the monopolist.
C) where price equals average total cost plus a fair rate of return on the invested capital of the monopolist.
D) where price equals average variable cost plus a fair rate of return on the invested capital of the monopolist.
E) at the minimum long-run average variable cost of the monopolist.