题干

小梅同学设计了如图所示的汽车有害尾气排放检测电路.其中,R为气敏电阻,它的阻值随有害气体浓度的增大而变小,电源电压恒定不变,R0为定值电阻,闭合开关,当有害尾气浓度增大时(  )

A:电压表示数变大,电流表示数变大

B:电压表示数变小,电流表示数变小

C:电压表示数变大,电流表示数变小

D:电压表示数变小,电流表示数变大

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D

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    Three years ago, when I entered my school for the first time, I was welcomed by students wearing white shirts with a badge (徽章) saying “Prefect” on them, who greeted me with the1“Welcome to Huaxia Middle School”. I was immediately impressed and2 I could be one of them. Then next year, in the summer of 2016, my wish3 when I was selected to be a prefect. Just like the ones4 me, I was to stand at the school gate and 5 new freshmen.

    So, you may wonder, what 6 is a prefect? Prefects are student leaders in our school. They're usually top students7 from higher grades to help teachers run the school 8 of the classroom9 you're chosen to be a prefect, you need to be a nearly perfect student. Becoming a prefect wasn't10 for me. I used to be sensitive and 11 caring too much about what others thought of me. But since I was12 to become a prefect, I tried my best to be more brave and hardworking, making rapid13in a year.

    The biggest benefit of being a prefect is that it teaches me to be14 and set an example for lower grade students. I was a member of the school soccer team, but I wasn't a good 15 and felt embarrassed about my poor 16. After having some students from lower grades join our team, however, I knew that I had to set a good example. So, I kept practicing my skills and 17 greatly.

    Being a prefect doesn't 18 mean I have a badge on my shirt. It also means that I have a hardworking attitude deep in my19“You can make it,” I always remind myself. Becoming a prefect has20 me to work harder and become an even better person.