A, b, it can be seen from the figure that the particle is biased to the lower left, that is to say, the particle is forced to the lower left. Because the direction of electric field lines is unknown, it is impossible to judge the electrical properties of particles, so A is correct and B is wrong;

C, as can be seen from the figure, in the process of particles from A to B, the electric field force does negative work, so the particle speed decreases, so it can be seen that the speed at B is smaller, so C is wrong;

D. If the electric field force does negative work, the electric potential energy will increase, so the electric potential energy at point B is larger, so D is wrong;

So choose a.