题干

研究电流跟电压、电阻的关系,用如图所示的电路,分“保持电阻不变”和“保持电压不变”两步进行,在“保持电阻不变”实验要求是(   )

A:保持R′的滑片位置不动

B:保持R不变,调节R′滑片到不同的适当位置

C:保持R的电压不变

D:保持电路中的电流不变

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答案(点此获取答案解析)

B

同类题3

阅读下面短文,掌握其大意,然后从各题所给的A、B、C、D四个选项中,选出最佳选项。

    No one is born a winner. People make themselves into winners by their own 1.

    I learned this lesson from a(n)  2 many years ago. I took the head 3job at a school in Baxley, Georgia. It was a small school with a weak football program.

    It was a tradition for the school's old team to play against the 4 team at the end of spring practice. The old team had no coach, and they didn't even practice to 5the game. Being the coach of the new team, I was excited because I knew we were going to win, but to my disappointment we were defeated. I couldn't 6 I had got into such a situation. Thinking hard about it, I came to 7 that my team might not be the number one team in Georgia, but they were 8me. I had to change my 9about their ability and potential.

    I started doing anything I could to help them build a little  10 .Most important, I began to treat them like 11 .That summer, When the other teams enjoyed their 12 ,we met every day and 13passing and kicking the football.

    Six months after suffering our 14on the spring practice field, we won our first game and our second, and continued to15.Finally, we faced the number one team in the state. I felt that it would be a 16for us even if we lost the game. But that wasn't what happened. My boys beat the best team in Georgia, giving me one of the greatest17my life!

    From the experience I learnt a lot about how the attitude of the leader can 18 the members of a team. Instead of seeing my boys as losers, I pushed and19them. I helped them to see themselves 20 ,and they built themselves into winners.

    Winners are made, but born.