题干

电梯为居民出入带来了很大的便利,出于安全考虑,电梯设置有超载自动报警系统,其工作原理如图所示,R1为保护电阻,R2为压敏电阻,其阻值随压力增大而减小.下列说法正确的是(  )

A:电磁铁是根据电磁感应原理制成的

B:工作时,电磁铁的上端为S极

C:超载时,电磁铁的磁性增强

D:正常情况下(未超载时),K与B接触

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答案(点此获取答案解析)

B,C

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    When I opened the box at my 12th birthday party, I couldn't believe my eyes. I had really gotten a mobile phone!

    As soon as I got to my school the next morning I 1off my phone and asked everyone for their2.

    It felt like I didn't even exist in that class any more. I wouldn't pay much attention to the teachers because I was too busy on my 3. Luckily I didn't get 4using it. I was pretty sure that the teacher didn't5that I stopped paying attention to her6a week later we took a test and I failed. To make matters 7, my mom had to sign the test.

    It was hard to show my mom the 8 . She was used to seeing As and Bs on my tests. Well, at last, I showed her and she couldn't 9it. She was angry.

    Weeks passed and my parents started to10the fact that I had a phone. They would say,“We have noticed that you never pay attention to us. It's like you have your own little 11now and we don't communicate as much with your phone.”

    I acted like they were wrong, but then I started to wonder if it was true that I was spending too much 12on the phone.

    A week later I tried 13 a whole day without a phone. I had so much 14because I was actually spending time with my family and paying attention to them. From that day, I had a different opinion towards phones.

    Phones really take you away from the rest of the world. I'm not saying that phones are15and not to use them, but you do have to spare some time to spend with your family. My phone took away time from my homework and from my family. I will keep using my phone, but I will have it under better control.