Assume for the United States that the opportunity cost of each airplane is 100 cars. Then which of these pairs of points could be on the United States' production possibilities frontier? a. (200 airplanes, 5,000 cars) and (150 airplanes, 4,000 cars) b. (200 airplanes, 10,000 cars) and (150 airplanes, 20,000 cars) c. (300 airplanes, 15,000 cars) and (200 airplanes, 25,000 cars) d. (300 airplanes, 25,000 cars) and (200 airplanes, 40,000 cars)