单项选择题

有以下等程序
#include ＜string. h＞
void f(char *s, char *t)
char k;
k=*s; *s=*t; *t=k;
s++; t--;
if(*s) f(s, t);main ()
char stt[10] ="abcdefg", *p;
p=str+strlen (str)/2+1;
f (p,p-2);
print f ( "%s\n", str);