质量为m的汽车在水平路面上行驶，所受阻力 恒定，汽车发动机的额定功率为P．若汽车以恒定的功率P行驶，汽车能达到的最大速度为 ____；如果汽车在某一时刻的速度为最大速度的 ，则此时汽车的牵引力为____，加速度为____．

许多老科学家、老艺术家在回忆自己的成长经历时，都非常怀念自己的中学时光，认为正是自己在中学阶段养成了认真学习的态度、勤奋钻研的精神、自主学习的习惯，为自己后来发展奠定了坚实的基础．这给我们的启示是（　　）

   We do the shopping on Sundays . I often go to the supermarket with my mother on Sunday morning in a car . Father likes fruit very much. We buy some red apples for him. Mother likes yellow bananas , but they're green. "Look! The strawberries are very nice, mum. Do you like them?" I say to Mum. "Yes, I like strawberries very much . " Mother buys some for herself. The oranges are very nice. Mother buys some for me . I like orange very much.
   We need some vegetables . The vegetables in the supermarket are very good . We buy some tomatoes, carrots and broccoli . I don't like broccoli, but my parents like it . I like carrots very much. We buy lots of carrots. After shopping , mother and I have some French fries, milk and ice cream. And then we go back home with the fruit and vegetables .