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{{B}}Electric Backpack{{/B}} Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hands free to do other things. Someday, if you don’t mind carrying a heavy load, your backpacks might also power your MF3 player, keep your cell phone running, and maybe even light your way home. Lawrence C. Rome and his colleagues from the University of Pennsylvania in Philadelphia and the Marine Biological Laboratory in Woods Hole, Mass., have invented a backpack that makes electricity from energy produced while its wearer walks. In military actions, search-and-rescue operations, and scientific field studies, people rely increasingly on cell phones, global positioning system (GPS) receivers, night-vision goggles, and other battery-powered devices to get aro A. To make the backpack more comfortable for the wearer. B. To put the backpack on the market. C. To test the advantage of the backpack. D. To promote the backpack in a newspaper or on television. 更多"{{B}}第二篇{{/B}}"的相关试题: [单项选择]{{B}}第二篇{{/B}}
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