以下结构体类型说明和变量定义中正确的是( )。

A．typedef struct
int n; char c; REC;
REC t1, t2;
B．struct REC;
int n; char c;;
REC t1, t2;
C．typedef struct REC;

int n=0; char c='A'; t1, t2;
D．struct
int n; char c; REC;
REC t1, t2;