C knows the answer by deducing D is not yelling out the answer.. q, L9 d3 [7 X! j/ O8 A
That means D is not sure the answer by seeing one white and one black. * _. o! \& ~/ Y7 VC 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.