code: def untag(tagged_sentence):
      """
      Given a tagged sentence, return an untagged version of that
      sentence.  I.e., return a list containing the first element
      of each tuple in *tagged_sentence*.
  
          >>> from nltk.tag.util import untag
          >>> untag([('John', 'NNP'), ('saw', 'VBD'), ('Mary', 'NNP')])
          ['John', 'saw', 'Mary']
  
      """
      return [w for (w, t) in tagged_sentence]
  
label_desc: Use image node_id 3 for calling a global function with example usage: untag(tagged_sentence) and returns: unknown