input: Write a function to sort an array in ascending order. The input is a list of integers, and the function should return the sorted list.
  
  assert sort_ascending([10, 3, 9, 1, 15, 2]) == [1, 2, 3, 9, 10, 15]
  assert sort_ascending([7, 2, 11, 5, 1]) == [1, 2, 5, 7, 11]
  assert sort_ascending([]) == []
  assert sort_ascending([3, 2, 1]) == [1, 2, 3]
  assert sort_ascending([1]) == [1]
output: def sort_ascending(arr):
      return sorted(arr)