求翻译：首先，自行车便于携带，其次它也是一种运动，有利于锻炼身体，因为越野自行车的快与刺激，对自己也是个突破和挑战，最重要的是它比汽车节省能源，不污染大气，为环保做出了贡献是什么意思？

First, the bike easy to carry, and secondly it is a sport, is conducive to exercise, because off-road bike fast and exciting, but also a breakthrough of their own and challenges, the most important thing is to save energy than cars do not pollute the atmosphere for environmental protection contribut

First of all, bicycle portability, followed by a movement, it is also conducive to physical activity, because mountain bikes with the fastest, to stimulate and challenge themselves, and it is also a breakthrough in the most important thing is that it is more than motor vehicle pollution of the atmos

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