C knows the answer by deducing D is not yelling out the answer. 9 D, d8 H4 O+ O$ I# v4 tThat means D is not sure the answer by seeing one white and one black.www3.tvboxnow.com. |, O5 y( A- S5 H( ?
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.