题目

阅读下面材料,根据其内容和所给段落开头语续写两段，使之构成一篇完整的短文。续写的词数应为150左右。Kindness is everywhere in our life. Some of us are just thankful and some help a lot.When browsing Wechat or other apps, there must be a few people asking for help like 'Oh, I forgot to bring my book back, can you take a picture on the text?' It's nothing at all for us to do more than lifting a finger, but most times, many people chose to turn off their phones or pretend that they didn't see the note. There will be somebody who answer him somehow, but he如图所示，在水平桌面上放置的足够长的平行金属导轨间串联了一个电容为C、充电后电荷量为Q0的电容器，两导轨间的距离为L；现将一质量为m的裸导体棒ab放在导轨上，方向与导轨垂直，整个装置处在竖直方向的匀强磁场中，磁感应强度为B；当闭合开关S后，导体棒ab将向右运动．若导体棒与导轨接触良好，忽略一切摩擦，则关于磁场方向以及闭合开关S后发生的现象，下列说法正确的是（　　）A．磁场方向竖直向上B．电容器的电荷量将逐渐减少，直到不带电C．导体棒ab先做匀加速运动，然后做匀减速运动，直到静止不动D．导体棒ab先做变加速运动，然后做匀速运动