input: Write a function to sort a list of items in descending order. Return the sorted list. If the input list is empty, return it as it is.
  assert sort_descending([3, 7, 5, 8, 10])==[10, 8, 7, 5, 3]
  assert sort_descending([])==[]
output: def sort_descending(lst):
      return sorted(lst, reverse=True) if lst else lst