题干

在某实验室中测量电源的电动势和内电阻,可以提供的器材有:

①待测电池:电动势E(约3V)、内电阻r(约1Ω)

②电流表:量程500μA,内阻r2=400Ω

③电流表:量程3A,内阻r1=0.1Ω

④滑动变阻器:阻值0﹣600Ω,额定电流0.5A

⑤滑动变阻器:阻值0﹣20Ω,额定电流2.5A

⑥电阻箱:9999.9Ω

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同类题5

阅读下面短文,从短文后各题所给的四个选项(A、B、C、D)中,选出可以填入空白处的最佳选项。

    A beggar was sleeping in the doorway of a fruit shop. The shop owner felt angry. He walked up to him and 1 him to go away in a rude manner, but the beggar did not seem to2 him and lay still there. The shop owner got much3, shouting that he was a beggar in disguise (假装) and4 cheated passers-by for money by making use of their kindness. At that time, it was the busiest moment of a day and the market was5with shoppers. They all blamed the beggar for6. Showing fear, the beggar7his face in an old blanket. What he received was bitter8rather than help.

    The next morning, it was drizzling. An old man, who went to the market early, found the beggar 9on the ground. He woke the beggar up and 10 asked whether he was cold or not, but the beggar made no 11. Then the old man12his hands gently, saying that they felt13. With these words, he ran home in a hurry, returned with a pile of14, picked out a sweater and urged the beggar to15 it on again and again. Seeing what happened, many other passers-by surrounded the beggar and gave him change one after another, showing16for him. It was not long before the beggar received a handful of 17.

    In many cases our behavior may have a great18 on the people around us because they are likely to19us. Therefore, we should pay special attention to what we do and say, trying to infect others with positive words instead of 20 ones.