input: Write a python function to sort a list of strings in alphabetical order.
  assert sort_strings(['apple', 'banana', 'pear', 'mango']) == ['apple', 'banana', 'mango', 'pear']
  assert sort_strings(['zebra', 'apple', 'orange', 'grape']) == ['apple', 'grape', 'orange', 'zebra']
  assert sort_strings(['car', 'bus', 'airplane', 'bicycle']) == ['airplane', 'bicycle', 'bus', 'car']
output: def sort_strings(strings):
      return sorted(strings)