C knows the answer by deducing D is not yelling out the answer. W* L3 z# i& g% m7 q! ^5.39.217.76That means D is not sure the answer by seeing one white and one black.5.39.217.76% ^5 ^5 S- H" o8 A+ h* N" F
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.