Power generators, which emit CO2, contribute abut 29 percent of the total emissions of all U.S. man-made greenhouse gases.
Almost a third of all CO2 emissions in the US are from machines that produce power. 
mnli hypothesis: Almost a third of all CO2 emissions in the US are from machines that produce power.  premise: Power generators, which emit CO2, contribute abut 29 percent of the total emissions of all U.S. man-made greenhouse gases.