C knows the answer by deducing D is not yelling out the answer.公仔箱論壇" P* p; d* A6 }+ ]4 v: y# V+ J
That means D is not sure the answer by seeing one white and one black.5.39.217.77/ z5 s1 ~* \& Q6 h2 T5 I4 D' k
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.