All else constant, if butter and margarine are substitute goods, then as the price of butter rises,
a. the demand for margarine will fall
b. the quantity of butter demanded will fall
c. the demand for butter will fall
d. the demand for butter will rise
e. butter and margarine will become complementary goods, provided that butter is a normal good

Which of the following statements is (are) true? i. free entry to a perfectly competitive industry results in the industry's firms earning zero economic profit in the long run, except for the most efficient producers, who may earn economic rent. ii. in a perfectly competitive market, long-run equilibrium is characterized by lmc < p < latc. iii. if a competitive industry is in long-run equilibrium, a decrease in demand causes firms to earn negative profit because the market price will fall below average total cost.