If a Regulatory Commission Wants to Establish a Socially Optimal

If a regulatory commission wants to establish a socially optimal price for a natural monopoly, it should select a price

A) at which the marginal cost curve intersects the demand curve.
B) at which marginal revenue is zero.
C) at which the average total cost curve intersects the demand curve.
D) that corresponds with the equality of marginal cost and marginal revenue.