C knows the answer by deducing D is not yelling out the answer. + s; E5 v7 U+ Q* J5 e% R7 rThat means D is not sure the answer by seeing one white and one black.公仔箱論壇% P3 w' R: s$ B; `/ x
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.