●Who knows ---- What is Jack?And tell me the reason!

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●Who knows ---- What is Jack?And tell me the reason!

●Who knows ---- What is Jack?And tell me the reason!
●Who knows ---- What is Jack?And tell me the reason!

●Who knows ---- What is Jack?And tell me the reason!
Jack?
A boy ?
杰克?
仆从?
千斤顶?
哈哈
"Jack:In practical mechanics, portable hand-operated device for raising heavy weights through short distances, exerting great pressures, or holding assembled work firmly in position!
千斤顶:在应用力学中,指携带方便、以手操作的装置,可将重物稍微抬高,能施加巨大压力,或将装配好的对象牢固地支撑在原地.