下列对枚举类型的使用的代码中错误的是（）。
A、enum {no, yes, none}answer;if (answer == yes){ printf("Yes\n");}
B、enum response{no = -1, yes = 1, none = 0};enum response answer;
C、answer = yes; printf("%d", answer);
D、answer = "yes";printf("%s", answer);