单选题：以下程序的输出结果是：

以下程序的输出结果是： @[A](2)
```
#include
void sub1(char a,char b)
{
char c;
c=a;
a=b;
b=c;
}
void sub2(char* a,char b)
{
char c;
c=*a;
*a=b;b=c;}
void sub3(char* a,char*b)
{
char c;
c=*a;
*a=*b;
*b=c;
}
int main()
{
char a,b;
a='A';b='B';sub3(&a,&b);putchar(a);putchar(b);
a='A';b='B';sub2(&a,b);putchar(a);putchar(b);
a='A';b='B';sub1(a,b);putchar(a);putchar(b);
return 0;
}
```
A. BABBAB
B. ABBBBA
C. BABABA
D. BAABBA




A.BABBAB
B.ABBBBA
C.BABABA
D.BAABBA


答案：A