What does the third paragraph imply [A] People will continue to use fossil fuels in spite of the benefit of hydrogen. [B] Fossil fuels are not renewable, and the amount of supply is limited. [C] Solar energy, just like fossil fuels, is also comparable to a savings account. [D] There is no limitation to the use of solar energy.
Although it is the most abundant element in the universe, hydrogen is not a primary energy source that exists in nature, as do crude oil and natural gas. Rather, it is an energy carrier ——a secondary form of energy that cannot be found freely in usable form, but has to be manufactured, like electricity. Today, most hydrogen is extracted from fossil fuels. In the future, hydrogen will be made from clean water and clean solar energy.
Hydrogen can match the effectiveness of fossil fuel in powering cars, planes, and ships and in heating homes, schools, and office complexes ——without creating pollution. When burned in an internal-combustion engine, hydrogen emits a virtually harmless water-vapor exhaust. When hydrogen is burned with atmospheric oxygen in an engine, the resulting emission is clean: no unburned hydrocarbons, no carbon monoxide or carbon dioxide.
Hydrogen is an essential component of fuel cells for vehicles and other applications. Fuel-cell engines can be more than twice as efficient as internal-combustion engines, argues Hoffmann. Fuel-cell engines electrochemically combine hydrogen and oxygen in a flameless process that produces heat, electricity, and distilled water. The fact that it is environmentally benign has made hydrogen energy an increasingly attractive alternative to fossil fuels as concerns about resource depletion and global warming have been growing.
"The question is no longer whether we are headed toward hydrogen, but how we should get there, and how long it will take," says Worldwatch Institute research associate Seth Dunn.