In the Long Run,all of a Firm's Costs Are Variable

In the long run,all of a firm's costs are variable.In this case the exit criterion for a profit-maximizing firm is to

A) shutdown if price is less than average total cost.
B) shutdown if price is greater than average total cost.
C) shutdown if average revenue is greater than average fixed cost.
D) shutdown if average revenue is greater than marginal cost.