以下选项中不能把s正确定义成结构体变量的是
A、struct student { int id; char name[20]; float score; }s;
B、struct { int id; char name[20]; float score; }s;
C、struct s { int id; char name[20]; float score; };
D、struct student { int id; char name[20]; float score; }; struct student s;