a long-run supply curve that is downward sloping indicates that the firms' atc curves shift up when the industry expands. shift down when the industry contracts. shift down when the industry expands. do not shift when the industry contracts.

When used-car dealers signal the quality of a used car with a warranty, a. buyers believe the signal because the cost of a false signal is high b. it is not rational to believe the signal because some used-car dealers are crooked c. the demand for lemons is eliminated d. the price of a lemon rises above the price of a good used car because warranty costs on lemons are greater than warranty costs on good used cars