input: Write a function to get elements at even positions from a list.
  assert get_elements([10, 20, 30, 40, 50]) == [10, 30, 50]
  assert get_elements([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == [1, 3, 5, 7, 9]
  assert get_elements([100, 200, 300]) == [100, 300]
output: def get_elements(lst):
      return lst[::2]