When entry barriers into a market are low, firms will tend to earn zero economic profit in the long run because

a. low entry barriers lead to rising costs.
b. profit-seeking entrepreneurs will not enter a market when entry barriers are low.
c. short-run profit attracts additional suppliers and drives down the market price.
d. consumers will refuse to pay more than the cost of producing a good once they find out the producer's per-unit costs.

C