题干

在水平轨道上有一辆实验车,其顶部装有电磁铁,电磁铁下方吸有一颗钢珠.在实验车向右匀速直线运动的过程中,钢珠因断电下落.如图所示是描述钢珠下落的四个示意图,图中虚线表示钢珠下落的路径.以实验车为参照物,正确描述钢珠下落路径的示意图是(   )

A:    

B:     

C:     

D:

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答案(点此获取答案解析)

C

同类题4

    I learned about life from an ant farm. When I was seven years old, my family created one. First, we put clean sand in a thin glass box and put the ants into it. Soon they got to work making tunnels. I was amazed that each one knew exactly what to do. With my mom's help, I kept a record of what happened each day and named the ants.
    One day when I had put my face close to the structure (building), accidentally I knocked it over, and all the tunnels fell in. Although the ants survived their earthquake, one by one they began to die. I was frightened as I watched them give up their tunnel-building to carry the bodies to a corner of the farm. My mother reported that the ants were dying of “frustration (挫折)”. They simply could not stand the reality that their tunnels had been destroyed.
    Although much time has passed, I still think of that ant farm. Over the years, I came to realize the ants have the spirit of teamwork. Working together, they were able to create an amazing world for themselves. I also learned that they should be admired for their hard work. Day in and day out, each worked at their task. The ant farm showed that teamwork and perseverance (毅力) are indeed the keys to success. But there was an even larger lesson that I did not realize until recently —Adversity (逆境) is a natural part of life, and must be accepted. Unlike the ants, humans cannot give up when they face disappointment.
    So I try to live my life like those hardworking ants. But, unlike them, I try not to let frustration defeat (击败) me. I will have to keep building my tunnels.