C knows the answer by deducing D is not yelling out the answer.公仔箱論壇& S6 s4 A* R# G. B0 y" T2 J; {% f& e
That means D is not sure the answer by seeing one white and one black.) |2 G. s5 l5 o' M/ b
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.