19.BC【解析】本题考查带电粒子在电场中的运动,目的是考查学生的推理能力。因粒子沿x轴正方向运动的过程中电势能减小故该过程中粒子所受电场力对其做正功选项A错误;因粒子电势能随位移变化的快慢恒定,故粒子所受电场力为恒力,可知该电场为匀强电场,粒子在电场中做匀加速直线运动,选项BC均正确;粒子做匀加速直线运动,单位时间内粒子的位移随时间的增大而增大,单位时间内粒子电势能的变化量随时间的增大而增大,选项D错误。

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

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