input: Write a function that takes a list of phone numbers and extracts only the ones that start with '08'. If the input list is empty, return an empty list.
  
  def extract_phone_numbers(phone_numbers):
      if not phone_numbers:
          return []
      return [number for number in phone_numbers if number.startswith('08')]
  
  assert extract_phone_numbers(['0834567', '0945678', '07123456', '08901234', '07890123'])==['0834567', '08901234']
  assert extract_phone_numbers(['0812345', '0898765', '0856789'])==['0812345', '0898765', '0856789']
  assert extract_phone_numbers(['0912345', '0798765', '0956789'])==[]
  assert extract_phone_numbers([])==[]
output: def extract_phone_numbers(phone_numbers):
      if not phone_numbers:
          return []
      return [number for number in phone_numbers if number.startswith('08')]