Other things equal,in which of the following cases would economic profit be the greatest?

A) An unregulated monopolist that is able to engage in price discrimination.
B) An unregulated,nondiscriminating monopolist.
C) A regulated monopolist charging a price equal to average total cost.
D) A regulated monopolist charging a price equal to marginal cost.

An unregulated monopolist that is able to engage in price discrimination would have the greatest economic profit because it would be able to charge different prices to different customers based on their willingness to pay, maximizing revenue and profit. The other options either involve regulation or non-discriminatory pricing, which would limit the monopolist's ability to maximize profit.