C knows the answer by deducing D is not yelling out the answer. 8 N5 P5 X* z' c+ BThat means D is not sure the answer by seeing one white and one black.公仔箱論壇$ c$ l3 L8 R' u" l! Y
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.