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  3. The Features of Solar and Wind Energy Solar and wind energy seem to have captured the public’s support as potentially being

The Features of Solar and Wind Energy Solar and wind energy seem to have captured the public’s support as potentially being

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问题                  The Features of Solar and Wind Energy
    Solar and wind energy seem to have captured the public’s support as potentially being the primary or total answer to our electric power needs despite the fact that solar cells and wind energy systems don’t always provide electric power.
    Solar cells and wind turbines are attractive because they are "renewables" and because they emit no C02, during operation. But because solar and wind electricity are available only part of the time that consumers demand power, they cannot provide energy " on demand", something that the public requires. We expect the lights to go on when we turn on a switch, and we do not expect our computers to shut down as nature dictates.
    Large-scale electric energy Storage with hydroelectric dams is a good way to solve the problem, but when we use hydroelectric dams for electric energy storage, we reduce their electric power output, which would otherwise have been used by consumers. In other words, we suffer a loss to gain power on demand from wind and solar.
    At locations without such hydroelectric dams, which are most places, solar and wind electricity systems must be backed up 100 percent by other forms of generation to ensure against blackouts. In today’s world, that backup power can only come from fossil fuels. Then the public will pay a large amount of money for solar and wind—paying once for the solar and wind system and again for the fossil fuel system.
    Finally, because solar and wind have the capacity to deliver only 30 to 40 percent of their full power ratings in even the best locations, they provide a C02 reduction of less than 30 to 40 percent, considering the fossil fuels needed for the backup. That’s far less than the 100 percent that many people believe, and it all comes with a high cost.
    The United States will need an array of electric power production options to meet its needs in the years ahead. Solar and wind will have their places, as will other renewables. Realistically, however, solar and wind will probably only provide a modest percentage of future US power. Some serious realism in energy planning is needed, especially from analysts who are not backing one horse or another.
What is the main idea of Para. 4?
选项 A、Solar and wind electricity system are costly.
B、Most places have no hydroelectric dams.
C、Fossil fuels can support the solar and wind energy.
D、Solar and wind systems should be abandoned.
答案A
解析 主旨大意题。由题干定位到第四段可知，本段主要讲没有可以储存能量的大坝的地区，需要对这两种发电系统进行支持，因此实际上造成了浪费。因此[A]“太阳能和风力发电系统花费非常昂贵”符合文意。[B]“大多数地区都没有水力发电站的大坝”．这是进行本段论述所需的先决条件，故排除；[C]“矿物燃料能够支持太阳能和风力发电”，这只是本段的一个事实，故排除；[D]“应该抛弃太阳能和风力发电系统”，与本段意思不符，故排除。
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