以下程序的输出结果是( ) #define sub1(char a, char b) {char c; c=a;a=b;b=c;} #define sub2(char *a, char b) {char c; c=*a;*a=b;b=c;} #define sub3(char *a, char *b) {char c; c=*a;*a=*b;*b=c;} 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); }