Ethanol is a derivative of corn and other grains. When burned as fuel, it emits significantly lower levels of carbon monoxide, a major atmospheric pollutant, than does gasoline. For that reason, environmentalists claim that ethanol is a better source of energy than gasoline. Which of the following, if true, most strongly supports the environmentalists' claim? ['Ethanol is comparable in price to gasoline.', 'When burned as fuel, ethanol does not release any pollutants at higher levels than does gasoline.', "Available supplies of corn are sufficient to supply several years' worth of ethanol.", 'Ethanol can be used as heating fuel.']