题目

Most Americans get what money they have from their work; that is, they earn an income from wages or salaries．The richest Americans, however, get most of their money from what they own ------- their stock, bonds, real estate, and other forms of property, or wealth．Although there are few accurate statistics to go by, wealth in American society appears to be concentrated in very few hands．More than 20 percent of everything that can be privately owned is held by less than one percent of the adult population and more than 75 percent of all wealth is owned by 20 percent of American adults． T如图所示，为某一点电荷所形成的一簇电场线，a、b、c 三条虚线为三个带电粒子以相同的速度从O点射入电场的运动轨迹，其中b虚线为一圆弧，AB的长度等于BC的长度，且三个粒子的电荷量大小相等，不计粒子重力，则以下说法正确的是A．a一定是正粒子的运动轨迹，b和c一定是负粒子的运动轨迹B．由于AB的长度等于BC的长度，故C．a虚线对应的粒子的加速度越来越小，c虚线对应的粒子的加速度越来越大，b虚线应的粒子的加速度大小不变D．b虚线对应的粒子的质量大于c虚线对应的粒子的质量