图中虚线是某电场的一组等势面．两个带电粒子从P点沿等势面的切线方向射入电场，粒子仅受电场力作用，运动轨迹如实线所示，a、b是实线与虚线的交点．下列说法正确的是

A．两粒子的电性相反

B．a点的场强小于b点的场强

C．a点的电势高于b点的电势

D．与P点相比两个粒子的电势能均减小

When the adjacency matrix method is used to store a graph, which of the statements is (are) true ( ) Ⅰ．the space required depends on the number of vertices Ⅱ．the apace required depends on the number of edges

A．None

B．Ⅰ only

C．Ⅱ only

D．Ⅰ and Ⅱ