input: Write a function to construct a nested loop in Python that prints out all combinations of elements from the list [1,2,3], [4,5,6], and [7,8,9]. The combinations should be printed out in a new line.
  assert nested_loop_combinations([1,2,3], [4,5,6], [7,8,9])==None
  assert nested_loop_combinations([10,11], [12,13], [14,15])==None
  assert nested_loop_combinations([], [], [])==None
output: def nested_loop_combinations(list1, list2, list3):
      for i in list1:
          for j in list2:
              for k in list3:
                  print(i, j, k)