C knows the answer by deducing D is not yelling out the answer. ) Z9 C7 \$ T1 k5 `$ ^# PThat means D is not sure the answer by seeing one white and one black. - x, X; o1 m2 {$ r' v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.