某同学用如图所示的电路进行小电机M的输出功率的研究，其实验步骤如下所述，闭合电键后，调节滑动变阻器，电动机未转动时，电压表的读数为U₁，电流表的读数为I₁；再调节滑动变阻器，电动机转动后电压表的读数为U₂，电流表的读数为I₂，则此时电动机的输出功率为    (    )    

阅读理解

    Many people like going shopping at weekends after five days'hard work．Supermarkets are good places for shopping．

    Before you go into the supermarket，get a trolley．Trolleys are usually outside the entrance(入口)．It's good to push your trolley around and take what you want．If you only plan to buy a few things，get a basket．Baskets are usually in the supermarket．You can buy different kinds of things in the supermarket．You can buy fruit and vegetables，meat and fish，bread and cakes，ice cream and magazines．

    There is a big supermarket near my home．My parents like shopping there but my sister Liz and I don't．There'll  be a sale in it on Saturday．My parents are going to buy some carrots and tomatoes．

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小明在九年级进行的六次数学测验成绩如下（单位：分）：76、82、91、85、84、85，则这次数学测验成绩的众数和中位数分别为（　 　）