input: Write a function to sort an array in ascending order. The function should take an array as input and return the sorted array. If the input array is empty, the function should return an empty array.
  assert sort_ascending([10, 3, 9, 1, 15, 2])==[1, 2, 3, 9, 10, 15]
  assert sort_ascending([])==[]
output: def sort_ascending(arr):
      return sorted(arr)