C knows the answer by deducing D is not yelling out the answer.5.39.217.771 W4 T0 u8 H( Q+ ?" v3 y
That means D is not sure the answer by seeing one white and one black. 7 U" z; X0 c$ c; jC 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.