a. -0.33gal/year; the average fuel consumption per year of a passenger car in the U. S. decreased by a third of a gallon per year. b. 0.33 gal/year; the average fuel consumption per year of a passenger car in the U. S. increased by a third of a gallon per year. c. 2.97 gal/year; the average fuel consumption per year of a passenger car in the U. S. increased by nearly 3 gal/year. d. -2.97 gal/year; the average fuel consumption per year of a passenger car in the U. S. decreased by nearly 3 gal/year.