Biofuels have been around for a long time and they are the least expensive renewable energy source.

生物燃料已经被使用了很长时间，并且它也是最便宜的可再生能源。

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Wind power has emerged as a viable renewable energy source in recent years - one that proponents say could lessen the threat of global warming.

风能是近几年呼声最高的可再生资源——其中一个原因在于，支持者们认为风能可以降低全球变暖的威胁。

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Recent years, wind power as a kind of clean and renewable energy source is drawing more and more attention.

近年来，风能作为一种清洁环保而储量丰富的可再生资源，日益成为各国研究的热点。

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If properly managed, clearing and replanting trees in a 30-year cycle creates both a renewable source of energy and maximum rubber production.

VOA: standard.2009.09.13

Dams offer a renewable energy source, providing the means for irrigation, transportation and flood protection.

CNN: Study opens floodgates on dam removal

China is already investing billions of dollars to substitute hydropower (which counts as a renewable energy source) for coal and gas in electricity generation.

FORBES: Pollution And Prosperity

Wind is the fastest-growing renewable energy source for electricity generation in the U.S., and DOE estimates that 20 percent of the energy consumed in the U.S. could come from wind power by 2030.

FORBES: 'Icebreaker': Offshore Wind Making Waves in Energy and Economic Development