In an effort to further reduce emissions, a government panel is considering several policy options. For the trends on the graph, which of the following policies could have the biggest long-term impact on lowering emissions? Subsidies supporting research to cut emissions by 10% Tax rebates for citizens who have one child per family A mandated switch to electric cars with a solar and wind-powered electrical grid to "fuel" the cars A high-speed train network that reduces vehicle miles traveled by 25%