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如图所示,直线A为电源的U—I图线,直线B为电阻R的U—I图线,用该电源和电阻组成闭合电路时,电源的输出功率和电路的总功率分别是( )
若ax﹣3b3与﹣3ab2y﹣1是同类项,则xy=____.
空气中能供给动植物呼吸的气体是( )