A, when the board is horizontal, because of the repulsion of B, A has friction force pointing to B; When the inclined plane rotates, when A is subjected to gravity, support and downward repulsion, the friction of A can only point to B; So, A is wrong;

B, according to the stress analysis of B, it can be seen that the friction force suffered by B at first points to A; When the chessboard rotates, B is subjected to gravity, supporting force and repulsive force. If the downward component of gravity is greater than the repulsive force, the friction force may be upward. Therefore, B is correct;

C, from the above stress analysis, it can be seen that with the increase of inclination angle, the downward force of A is greater than that of B; Therefore, A should slip first; So, c is wrong;

D. If the distance between A and B decreases, the repulsion between the two magnets will increase, but the effect is the same as that in C, so A slides first; So, d is wrong;

Therefore, choose: B.