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阅读理解Nikola TeslaLong overshadowed in public memory by his one-time employer, Thomas Edison, Tesla (1856?1943) was a brilliant scientist and engineer who earned more than 700 patents. He is most famous for developing alternating current (交流电), but his work also led to advances in wireless communications, lasers, X-rays, radar, lighting, robotics, and much more.Tesla was born to Serbian parents in what is now Croatia, but he emigrated(移民) to the U.S. as a young man, where he eventually became a naturalized citizen. Besides Edison, who later became his bitter rival, Tesla often 一排共9个座位，甲、乙、丙三人按如下方式入座，每人左、右两旁都有空座位，且甲必须在乙、丙两人之间，则不同的坐法共有      种。