[单选] 

33、下列（    ）对结构类型变量定义是错误的。

struct teacher  {int num;   int age;   }teach1;

struct {int num;   int age;   }teach1,teach2;

struct  {int num;   int age;   }teacher;   struct teacher teach1;

struct teacher {int num;   int age;   };   struct teacher teach1;