② If B is wrong, it may be: 1. It is not as good as C, and it is the worst. Contradictions with what Ding said; 2. It is better than C, which contradicts what C said. So b is right.

If c is wrong, c is not the best. At this time, the ranking is: A > C > B > Men.

If Ding is wrong, Ding is not the worst. Then at least one of the remaining A, B and C must be the worst. Obviously, C can't be the worst, so one of A and B is the worst. Contradictions with what A and B said.

So it can only be that C is wrong. The grades of the four people from high to low are: a, c, b and d.