有以下程序：
#include ＜stdio.h＞
int fun(int a，int b)
if(b==0) return a；
else return (fun(--a,--b))；

main()
printf("%d\n", fun(4, 2));
程序的运行结果是( )。

A．1,2,3,4,5,6,7,8,9,0,
B．2,1,4,3,6,5,8,7,0,9,
C．0,9,8,7,6,5,4,3,2,1,
D．0,1,2,3,4,5,6,7,8,9,

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;