The correct option is C Both of them
Both of them.
1. Increasing the energy efficiency of combustion engines can help to reduce pollution. If vehicle engines are more economical in terms of an increased number of miles per gallon of fuel, then overall less fossil fuel is burned.
2. driving cars and trucks also produces significant amounts of nitrogen oxide emissions. To help cut down on air pollution from cars, you can consolidate driving trips, carpool or take public transportation, such as buses and trains.