C knows the answer by deducing D is not yelling out the answer.
% B% }5 K: h2 R# w F6 atvb now,tvbnow,bttvbThat means D is not sure the answer by seeing one white and one black.
4 S8 V; U* f6 q1 E$ O! Z8 N1 J9 @C saw B is wearing the white, hence he is wearing the black |