Vehicles powered by hydrogen fuel cells are, in theory, pollution-free but their popularity has been compromised by the difficulty of generating hydrogen cheaply and plentifully.

从理论上讲，氢燃料电池驱动的汽车是无污染的，但由于氢难以廉价、大量地生产，这种汽车在普及方面打了折扣。

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Solar energy is lauded as an inexhaustible fuel source that is pollution and often noise free. The technology is also versatile.

太阳能被称为是取之不尽的能源，没有污染，通常也没有噪声，而且用途广泛。

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Magnesia chrome bricks must be replaced by chrome free basic bricks because of chrome pollution and for utilization of substituting fuel in cement kiln.

为了消除铬公害以及替代燃料的使用，研制水泥窑用碱性砖的无铬化势在必行。

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In the long-term, it could have a glittering future for it leads the world in pollution-free hydrogen fuel-cell cars.

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