C knows the answer by deducing D is not yelling out the answer. ( O6 h& e7 T2 {* L) W: s( YThat means D is not sure the answer by seeing one white and one black. d8 Q+ ]& q4 V" s) a! D& c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.