input: Write a python function to extract characters 'a', 'b', 'c', 'd', and 'e' from a string and print each on a new line.
  assert extract_abce("abcdefg") == "a\nb\nc\nd\ne\n"
  assert extract_abce("hello world") == "e\n"
  assert extract_abce("xyz") == ""
output: def extract_abce(s):
      result = ""
      for char in s:
          if char in "abcde":
              result += char + "\n"
      return result