Renewable Energy Sources Today petroleum(石油)provides around 40% of the world’s energy needs, mostly fuelling automobiles. Co

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问题                         Renewable Energy Sources
    Today petroleum(石油)provides around 40% of the world’s energy needs, mostly fuelling automobiles. Coal is still used, mostly in power stations, to cover one-quarter of our energy needs, but it is the least efficient, unhealthiest and most environmentally damaging fossil fuel(矿物燃料). Natural gas reserves could fill some of the gap from oil, but reserves of that will not last into the 22nd century either. Most experts predict we will exhaust easily accessible reserves within 50 years. Less-polluting renewable energy sources offer a more practical long-term energy solution. " Renewable" refers to the fact that these resources are not used faster than they can be replaced.
    Hydroelectric(水力发电的)power is now the most common form of renewable energy, supplying around 20% of world electricity. China’s Three Gorges Dam is the largest ever. At five times the size of the U. S. ’s Hoover Dam, its 26 turbines(涡轮机)will generate the equivalent energy of 18 coal-fired power stations. It will satisfy 3% of China’s entire electricity demand.
    In 2003, the first commercial power station to use tidal(潮汐的)currents in the open sea opened in Norway. It is designed like windmill(风车), but others take the form of turbines.
    As prices fall, wind power has become the fastest growing type of electricity generation— quadrupling(翻两番)worldwide between 1999 and 2005. Modern wind farms consist of turbines that generate electricity. Though it will be more expensive, there is more than enough wind to provide the world’s entire energy needs. Wind farms come in onshore and offshore forms. They can often end up at spots of natural beauty, and are often unpopular with residents. And turbines are not totally harmless—they can interfere with radar, alter climate and kill sea birds. Scotland is building Europe’s largest wind farm, which will power 200, 000 homes. The U. K. ’s goal is to generate one-fifth of power from renewable sources, mainly wind, by 2020. But this may cause problems, because wind is unreliable.
One of the problems with wind farms is that______.

选项 A、there is not enough wind
B、wind is not reliable
C、they can only be built on the sea
D、they might influence the world economy

答案B

解析 文章最后一句话指出英国到2020年五分之一的电力来自风力发电的目标会产生问题,因为风是不稳定、不可靠的(unreliable),本题正确答案为B。
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