How can a government regulate a monopoly firm making supernormal profits so that a “socially optimal” outcome obtains:

(A) set the firm’s price (and quantity) corresponding to the point where the MC
curve intersects the AC curve from below.
(B) set the firm’s price (and quantity) corresponding to the point where the MC curve
intersects the MR curve from below.
(C) set the firm’s price (and quantity) corresponding to the point where the MR curve
intersects the AC curve and AC>MR after that point.
(D) set the firm’s price (and quantity) corresponding to the point where the AR curve
intersects the MC curve and MC>AR after that point.