C knows the answer by deducing D is not yelling out the answer.www3.tvboxnow.com% r9 w5 w8 x/ y( @4 u. `
That means D is not sure the answer by seeing one white and one black. 7 o3 A6 m$ G1 u; ]) |, @& S2 eC 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.