A. During the downward movement of the ball, it is influenced by gravity and electric field force. During the movement from A to B, both gravity and electric field force do zero work, so the speed of reaching point B is exactly zero, so it can reach point B, so A is right and B is wrong;

C. if q is negatively charged, there is: FN at the lowest point? Mg = mv2r, the solution is: FN=mg+mv2r, so the pressure on the track can't be zero, so C is wrong;

D if q is a positive charge, at the lowest point: fn+mg = mv2r, the solution is: FN+mg=mv2r? Mg, so FN can be less than gravity, so d is wrong.

So choose one