C knows the answer by deducing D is not yelling out the answer. 5 q/ q9 P3 _. D: i0 u8 a2 t0 s- _That means D is not sure the answer by seeing one white and one black.2 q+ ^2 s" h& S
C saw B is wearing the white, hence he is wearing the black
C, because he saw B's hat is white and he knows D can see the color of B's and his hat. If B and his hat has the same color, D would speak out. But D kept silent, so C knows that his hat's color must be different.