Economist: The most economically efficient way to reduce emissions of air pollutants is to tax them in proportion to the damage they are likely to cause. But in Country Y, many serious pollutants are untaxed and unregulated, and policy makers strongly oppose new taxes. Ttherefore, the best way to achieve a reduction in air pollutant emissions in Country Y would be to institute fixed upper limits on them. Which of the following is an assumption of the economist's argument? ['Policy makers in Country Y oppose all new taxes equally strongly, regardless of any benefits they may provide.', 'Policy makers in Country Y strongly favor reductions in air pollutant emissions.', "Country Y's policy makers believe that air pollutant emissions should be reduced with maximum economic efficiency.", 'Policy makers in Country Y do not oppose setting fixed upper limits on air pollutant emissions as strongly as they oppose new taxes.']