Oil and coal, which have brought about modern industry, are limited resources and destined to be exhausted someday. Moreover, combustion of oil or coal causes various kind of pollution. That's why the advanced nations are groping for the clean alternative energy sources since the oil crisis. There are many candidates for it, such as nuclear power, photovoltaic power, wind power, waterpower generation, but it is my considered opinion that methane is the best alternative energy sources. I'll tell you the reason for it.