题干

一长直铁芯上绕有一固定线圈M,铁芯右端与一木质圆柱密接,木质圆柱上套有一闭合金属环N,N可在木质圆柱上无摩擦移动.M连接在如右图所示的电路中,其中R为滑动变阻器,E1和E2为直流电源,S为单刀双掷开关.下列情况中,可观测到N向左运动的是(  )

A:在S断开的情况下,S向a闭合的瞬间

B:在S断开的情况下,S向b闭合的瞬间

C:在S已向a闭合的情况下,将R的滑动头向c端移动时

D:在S已向a闭合的情况下,将R的滑动头向d端移动时

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答案(点此获取答案解析)

C

同类题2

完型填空。

Tom and Steve were twin brothers. Tom loved to play basketball. But Steve loved to read books. One day Tom was playing basketball 21  he fell and broke his leg. When they took him to the hospital, the doctor said he wouldn’t be able to play for six months. Steve went 22  him to and brought him books on basketball. At first Tom wasn’t going to read them. Then he began to read them and 23 that there were ways he could play basketball better. He began to think that books weren’t 24  .

   When Tom’s leg started getting better, Steve would help him by going for walks with him.  25 Tom’s doctor said he could start playing basketball again. Then Tom showed Steve how to toss(投)for baskets. Steve found that he enjoyed it.

   Then Tom was ready to 26  the basketball games. Steve went to watch the games and enjoyed himself. They then  27 practiced basketball and read books together.

   So you can see, when  28  happens, something good may also happen. Steve showed Tom about books and Tom showed Steve about basketball.

So you can also  29 showing others something that you like to do and they can show you something that they like to do. 30 you can find new things to do.

21A. until              B. when            C. after           D. where

22A. on seeing          B. to call            C. to visit         D.to look

23A. saw              B. looked            C. read           D. found

24A. good             B. bad              C. better           D. worse

25A. But              B. However          C. Finally         D. So

26A. take              B. win              C. lose            D. join in

27A. always            B. never            C. seldom          D. much

28A. anything good      B. something nice     C. something bad   D. anything wrong

29A. try               B. practice           C. enjoy          D. like

30A . On the way       B. By the way        C. In a way       D. In this way