C knows the answer by deducing D is not yelling out the answer.$ s) c4 P! X( l7 a, \6 X* }0 g
That means D is not sure the answer by seeing one white and one black. 3 l( a4 L* d* Z3 R$ NC 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.