In Which of the Following Ways Can a Government Assure

In which of the following ways can a government assure that a natural monopolist earns zero economic profit?

A) by setting the price equal to marginal cost
B) by setting the price equal to average total cost
C) by setting the price lower than the average total cost
D) by asking the monopolist to produce where marginal cost is equal to marginal revenue
E) by asking the monopolist to produce where marginal cost is equal to average total cost