题干

如图电路中,电源电动势为E、内阻为r,R0为定值电阻,电容器的电容为C.闭合开关S,增大可变电阻R的阻值,电压表示数的变化量为△U,电流表示数的变化量为△I,则(  )

A:电压表示数U和电流表示数I的比值不变

B:变化过程中△U和△I的比值保持不变

C:电阻R0两端电压减小,减小量为△U

D:电容器的带电量减小,减小量为C△U

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B

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    I grew up poor. We had little money, but plenty of love and attention. I understood that no matter how poor a person was, he could still afford a dream. My dream was athletics.

    By the time I was sixteen, I was good at baseball and football. My high-school coach was Ollie Jarvis. He not only believed in me, but taught me the difference between having a dream and showing conviction(信念).

    One summer a friend recommended me for a summer job. This meant a chance for money in my pocket — cash for dates with girls, certainly, money for a new bike and new clothes, and the start of savings for a house for my mother.

    Then I realized I would have to give up summer baseball to handle the work schedule, and that meant I would have to tell Coach Jarvis I wouldn't be playing. I was dreading(害怕) this, but my mother said, “If you make your bed, you have to lie in it.”

    When I told Coach Jarvis, he was as mad as I expected him to be. “Your playing days are limited. You can't afford to waste them,” he said.

    I stood before him with my head hanging, trying to think of the words that would explain to him why I dreamed of buying my mom a house.

    “How much are you going to make at this job, son?” he demanded.

    “Three twenty-five an hour,” I replied.

    “Well,” he asked, “is $3.25 an hour the price of a dream?”

    That question laid bare for me the difference between wanting something right now and having a goal. I devoted myself to sports that summer, and within the year I was drafted by the Pittsburgh Pirates to play rookie-league ball, and offered a $20,000 contract. I signed with the Denver Broncos in 1984 for $1.7 million, and bought my mother the house of my dream.