如图所示，酸甜多汁的水果点亮了一排发光二极管，在这个简单的电路中水果相当于____，如果想控制这个电路的通断，还应在电路中安装____．

如图，正方形卡片A类，B类和长方形卡片C类若干张，如果要拼一个长为（a+2b），宽为（a+b）的大长方形，则需要C类卡片____张．

椐统计至2008年5月31日，扬州市人口总数是四百八十九万六千人，这个数写作____，改写成用“万”作单位的数是____万，省略“万”后面的尾数是____万．

学生问：“有甲乙两人，甲很干净，乙很脏。如果请他们洗澡，他们中间谁会洗？”老师答：“这里有四种可能：一是甲洗，因为他有爱干净的习惯；二是乙洗，因为他需要；三是两人都洗，一个是因为习惯，一个是因为需要；四是两人都不洗，因为脏人没有洗澡的习惯，干净人不需要洗。”根据材料，这位老师最有可能是

    Martin had just finished high school. He would go to college at the far end of the city. He didn't want to live there, and he didn't want to take the bus either. So his father agreed to buy him a car.
    His father spent all his summer teaching him how to drive, from the ABC to the XYZ. Thinking of the great feeling of driving a new car, Martin learned very quickly, and received his driver's license just before his eighteenth birthday.
    The second day, all the family, and their dog, went to a car shop. Martin spent almost all the morning going from one car to another. Finally he saw a red Blue Bird. He had a test drive on the open ground, and called out, “This is what I want, Dad!” When everything was done, they were ready to leave.
    Martin climbed into the front seat. He said excitedly, “It's my first day driving alone. Dad, Mom, and Poo! Enjoy it!”
His dad immediately took the back seat, right behind the new driver. Martin wondered why his father chose that seat, for his father always enjoyed looking in front.
    So he said, smiling, “I'm sure you're back there to have a change after all those weeks of sitting in the front seat teaching me how to drive.”
    “No,” Dad replied, “Do you remember what you did to me all those years when I took you to and from school? I am sitting here to hit and kick the back of your seat all the way!”