以下对结构体类型变量td的定义中，错误的是

A．typedef struct aa
int n;
float m;
AA;
AA td;
B．stmct aa
int n;
float m;
td;
stmct aa td;
C．struct
int n;
float m;
aa;
struct aa rd;
D．struct
int n;
float m;
td;