gas-efficient may blubber more kerosene & rest kerosene requires shade kerosene ->  gas-efficient engines will burn less gasoline  gas-efficient engines will burn less gasoline & shade kerosene is a sink of land purity ->  gas-efficient engines will cause less air pollution  gas-efficient engines will cause less air pollution & an combines is a whole of an shepherd -> using a gas-efficient engine in automobiles will cause less air pollution