Another answer might be, well, it came from a sort of lone genius working in his garage, who, working away on different kinds of bikes, comes up with a bike out of thin air.
另外一种回答可能是，嗯，山地车来自于一个孤独的天才。 他在他的车库里面， 研究了很多种不同的自行车， 然后就凭空想像出了这么一种新型的自行车。