C knows the answer by deducing D is not yelling out the answer.5 }$ u0 L/ d$ g0 m+ u
That means D is not sure the answer by seeing one white and one black.6 D! ]2 B' @- g9 R; z( T" S6 s
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.