Alice and John are in the music club at their school. Alice plays the violin and John plays the drums. There are two groups in the school music club: the training (训练) group and the concert(音乐会) group. Everyone starts in the training group!

     "When I first started to play the violin it sounded terrible!" Alice said. "My family asked me to practice outside."

    After a year's practice, Alice and John play much better now. They are both in the concert group and they are learning more difficult music. "We're learning the music from the film Pirates of the Caribbean. It sounds fantastic!" John said. "Playing in the club with other kids is a lot of fun."

    Playing an instrument (乐器) is not only fun. It also helps children learn to concentrate (集中注意力). "I have to concentrate when I'm practicing," Alice said. "And now it's easier for me to concentrate on my schoolwork."

    Playing an instrument can also help children become more confident (自信的). As John said, "I was scared when I played in front of a lot of people for the first time. But now I really enjoy it."

计算：（4x²y²﹣2x³y）÷（﹣2xy）=____.

如图中的三个电路电源电压均相同且保持不变，灯泡的规格相同，忽略温度对电阻的影响．当开关闭合后，a、b、d三盏灯实际功率的大小关系式正确的是（　　）