If the firm is making economic profit in the short-run, what will happen to the firm in the long run?

a. More firms will enter the industry, thus driving down price until profit equals zero.

b. More firms will enter the industry, thus lowering cost and raising profit because of economies of scale.

c. More firms will enter the industry, thus increasing average total cost but leaving price unchanged until profit equals 0.

d. Firms will leave the industry, thus increasing price until profit equals zero