What is the output of the following program?

#include<stdio.h>
void f1(char *x, char *y) {
  char *t1;
  t1 = x; x = y; y = t1;
}
void f2(char **x, char **y) {
  char *t1;
  t1 = *x; *x = *y; *y = t1;
}
int main() {
  char *a = "ONE", *b = "TWO";
  f1(a, b);
  printf("%s %s ", a, b);
  f2(&a, &b);
  printf("%s %s", a, b);
  return 0;
}

1. AONE TWO TWO ONE
2. BTWO ONE ONE TWO
3. CONE TWO ONE TWO
4. DTWO ONE TWO ONE

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