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  3. There is little debate about the first development of the energy system of the 22nd century that most of the energy produced on

There is little debate about the first development of the energy system of the 22nd century that most of the energy produced on

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问题         There is little debate about the first development of the energy system of the 22nd century that most of the energy produced on a large scale will be in the form of electric power. Thus, most present concepts for major long - term energy sources (solar, geothermal, fusion) are based upon electric power production at central plants.
        The second major development is the potential use of hydrogen as both a basic fuel to replace natural gas and as part of a general system to convert, store and transmit electric energy over long district by fuel cells, or it could be used directly as a fuel for commercial, industrial of transportation purposes.
        Although hydrogen seems likely to play a major role in the future as a form of energy transport and storage, other processes may also be useful. Here we note only two possibilities.
        Fly wheels: it appears to be workable to construct flywheels of almost any needed size that would be efficient converters(93—95 percent) in first storing and then releasing electric power. In addition, the kinetic (动力的) energy of rotation is easily converted to alternating electric power. But the engineering is at an early state of development, and a decade or more may pass before this potential can be reliably estimated.
        Batteries and fuel cells: some of many batteries being developed today look quite promising. Within a decade or two, a battery-operated auto might even become competitive with today’ s vehicles , at least for driving ranges up to 200 miles. An electric automobile would be pollution-free, and would probably be more energy-efficient than the internal-combustion(内燃) engine.
        A fuel cell (which may be considered a hydride battery) with about 40 percent conversion efficiency is expected to enter power production on a large scale within about five years. Unlike steam-powered generators, fuel cells can be made large or small and their efficiency in operation is essentially independent of the loading. Thus they may avoid waste of the distribution costs of electric power as well as provide pollution-free power and offer opportunities for using the "waste heat" effectively.
The energy we use most today is___________.
选项 A、solar energy
B、geothermal energy
C、hydrogen
D、electricity
答案D
解析 根据文章第一段第一句话可得出现在我们用得最多的能源是电力，答案为D。
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