input: Write a function to construct a nested loop that prints out every combination of elements from three given lists, each element on a new line. The function should take three lists as input and print the combinations by nesting the loops appropriately.
  assert nested_loop_combinations([[1,2,3], [4,5,6], [7,8,9]])==None
  # Expected output:
  # 1 4 7
  # 1 4 8
  # 1 4 9
  # 1 5 7
  # 1 5 8
  # 1 5 9
  # 1 6 7
  # 1 6 8
  # 1 6 9
  # 2 4 7
  # 2 4 8
  # 2 4 9
  # 2 5 7
  # 2 5 8
  # 2 5 9
  # 2 6 7
  # 2 6 8
  # 2 6 9
  # 3 4 7
  # 3 4 8
  # 3 4 9
  # 3 5 7
  # 3 5 8
  # 3 5 9
  # 3 6 7
  # 3 6 8
  # 3 6 9
  assert nested_loop_combinations([[1], [2], [3]])==None
  # Expected output:
  # 1 2 3
output: def nested_loop_combinations(lists):
      for i in lists[0]:
          for j in lists[1]:
              for k in lists[2]:
                  print(i, j, k)