code: def _normalize_answer(text: str) -> str:
      
  
      parts = [_white_space_fix(_remove_articles(_normalize_number(_remove_punc(_lower(token)))))
               for token in _tokenize(text)]
      parts = [part for part in parts if part.strip()]
      normalized = ' '.join(parts).strip()
      return normalized
docs: Lower text and remove punctuation, articles and extra whitespace.