C knows the answer by deducing D is not yelling out the answer.& v4 X( x2 G' p, b7 D3 Z
That means D is not sure the answer by seeing one white and one black. " x1 I% U4 Y7 [) y* F8 Z: [* g% ^公仔箱論壇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.