C knows the answer by deducing D is not yelling out the answer.9 @/ z x9 l4 s. E) ]2 }9 d
That means D is not sure the answer by seeing one white and one black.. f1 C! y6 F: `+ a! A! O
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.