A, in the process of falling, athletes are subjected to gravity and resistance. According to the theorem of kinetic energy, the increase of kinetic energy is equal to (mg-F)h, so A is wrong;

B, the work done by gravity is mgh, and the work done by gravity is equal to the decrease of gravitational potential energy, so the gravitational potential energy decreases mgh, so B is correct;

C, d, the total work done by forces other than gravity is equal to the increase of mechanical energy. In addition to gravity, athletes overcome resistance to do work as Fh, so mechanical energy reduces Fh, so C is wrong and D is wrong;

So choose B.