题目内容：
根据下列文章,请回答题。Renewable Energy SourcesToday petroleum 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. Natural gas reserves could plug 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. We could fast reach an energy crisis. We need to rapidly develop sustainable solutions to fuel our future. Less-polluting renewable energy sources offer a more practical long-term energy solution. They may benefit the world's poor too. "Renewable" refers to the fact that these resources are not used faster than they can be replaced.The Chinese and Romans used watermills over 2000 years ago. But the first hydroelectric (水电的) dam was built in England in 1870. Hydroelectric power is now the most common form of renewable energy, supplying around 20% of world electricity. China's Three Gorges Dam, which has just been completed, is the largest ever. At five times the size of the US'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. Surprisingly, some argue that hydroelectric dams significantly contribute greenhouse gases.
In 2003, the first commercial power station to harness tidal currents (潮汐发电) in the open sea opened in Norway. It is designed like windmills, but others take the form of turbines.
As prices fall, wind power has become the fastest growing type of electricity generation - quadrupling (变成四倍) 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 benign (无害的) - they can interfere with radar and leave a significant ecological footprint, altering climate and killing sea birds. Migrating birds may have more luck avoiding them. Scotland is building Europe's largest wind farm, which will power 200,000 homes. The UK'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.According to the passage, the most popular form of renewable energy in the world is_________ A．hydroelectric powe
B．solar energ
C．wind powers
D．tidal powe
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