Under What Circumstances Will a Profit-Maximizing Firm That Is Operating

Under what circumstances will a profit-maximizing firm that is operating in the short run sell an additional unit of output?

A) as long as doing so reduces the firm's per-unit costs
B) as long as doing so adds more to revenue than it adds to cost
C) as long as there is additional plant capacity with which to produce
D) as long as doing so reduces the firm's marginal costs