walking to work is one way of helping improve air quality.; air pollution is only caused by human activity.; acid rain is the direct result of acid released by burning fossil fuels.; humans are not the only animals that pollute the air.; the principal limitation of wind power is unpredictability.; which government agency would you expect to be most concerned with the impacts of pollution?; wind, solar and geothermal power are called renewable energy sources because _______.; pollution in the will have the greatest effect on human health.