题目

Many of you are studying hard because you have to compete with many others in the upcoming national college entrance exam. But it may not occur to you that one of your competitors is a robot. An artificial intelligence(AI) robot will take part in the 2017 National College Entrance Exam, reported China Daily.   “The robot will sit three exams: math, Chinese, and a comprehensive test of liberal arts (文科), which includes history, politics and geography,” Lin Hui, CEO of an AI company in Chengdu. Like the others who take the exam, the robot will have to finish the tests in the giv13．一个带电粒子，沿垂直于磁场方向，射入匀强磁场中，粒子的一段径迹如图所示，径迹上的每一小段都可以近似看成圆弧．由于带电粒子使周围的空气电离，粒子的能量逐渐减小而带电量不变．不计粒子重力，从图中情况可以确定（　　）A．粒子是带正电的，它所受的洛仑兹力大小不变B．粒子是带正电的，它是由a点运动到b点C．粒子是带负电的，它所受的洛仑兹力大小逐渐增大D．粒子是带负电的，它是由a点运动到b点