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  3. Electric Backpack Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hand

Electric Backpack Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hand

admin2016-08-16  7
问题                         Electric Backpack
    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 MP3 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 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(接收器),night-vision goggles(夜视镜),and other battery-powered devices to get around and do their work. The backpack’ s electricity-generating feature could greatly reduce the amount of a wearer’ s load now devoted to spare batteries.
    The backpack’ s electricity-creating powers depend on springs used to hang a cloth pack from its metal frame. The whole pack moves up and down as the person walks. A special mechanism converts movements of the pack to electricity, which can be as much as 7.4 watts.
    Unexpectedly, tests showed that wearers of the new backpack alter their gaits(步法)in response to the pack’ s oscillations(摆动),so that they carry loads more comfortably and with less effort than they do ordinary backpacks. Because of that surprising advantage, Rome plans to commercialize both electric and nonelectric versions of the backpack.
    The backpack could be especially useful for soldiers, scientists, mountaineers(登山运动员), and emergency workers who typically carry heavy backpacks. For the rest of us, power-generating backpacks could make it possible to walk, play video games, watch TV, and listen to music, all at the same time. Electricity-generating packs aren’ t on the market yet, but if you do get one eventually, just make sure to look both ways before crossing the street!
Backpacks are very convenient because they an______.
选项 A、change your gaits
B、reduce your load
C、free your hands
D、control your MP3 player
答案C
解析 由文章开头“Backpacks are convenient．They can hold your books，your lunch，and achange of clothes，leaving your hands free to do other things”可知，背包可以装许多东西，这样就可以解放双手做其他事情。故选C。
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