Why have vehicle emissions of pollutants decreased in the past 20 years? Check All That Apply The EPA has imposed limits on emissions.The EPA has imposed limits on emissions. Fuel economy has improved overall.Fuel economy has improved overall. All vehicles are using less gas because they have to have at least 30 miles-to-the-gallon (MPG) efficiency.All vehicles are using less gas because they have to have at least 30 miles-to-the-gallon (MPG) efficiency. The catalytic converter became mandatory in 2020