A, proton electric field force points to the curve side of trajectory, so proton electric field force points to negative charge, so the charge at point B must be negative charge, so A is correct;

B, the electric field force of protons has nothing to do with the speed direction, so it is impossible to judge whether protons move from M to N or from N to M, so B is wrong;

C, d, because ao > ob, φM is greater than φ n according to the distribution characteristics of electric field lines and equipotential surfaces with the same amount of different point charges;

The potential of positive charge is large at the position with high potential, so the potential of proton at point M is greater than that at point N; So, C is wrong and D is right;

Therefore: ad.