When moving down along a straight-line demand curve:
a) the elasticity of demand stays the same.
b) the elasticity of demand changes from inelastic to elastic.
c) total revenue always stays the same.
d) the elasticity of demand changes from elastic to inelastic.

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.