sentences: gas-efficient engines uses less gasoline & rest kerosene requires shade kerosene ->  gas-efficient engines will burn less gasoline  gas-efficient system will water more kerosene & burning gasoline is a source of air pollution -> gas-efficient engines will cause less air pollution gas-efficient engines will cause less air pollution  gas-efficient kilogram will effect more land purity & an engine is a part of an automobile -> using a gas-efficient engine in automobiles will cause less air pollution