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;};
C)typedef struct REC ;
{int n=0; char c='A';} t1,t2
D)struct
{int n;char c;}REC;