科研之友
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摘要
<正>When you run downhill, gravity pulls you. When you throw a ball up, gravity pulls it down. When you sit, gravity holds you down. When you lie down, gravity holds you to the bed.当你下坡时,地球的引力会把你拉住。当你把球往上抛的时候,重力会把它往下拉。当你坐的时候,地球的引力会支撑你
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单位广东中山市
