code: def word_for_char(string_matrix: List[List[str]], character: str) -> List[str]:
      
      return [word
              for sentence in string_matrix
              for word in sentence
              if character in word]
docs: Diagnostic function, collect the words where a character appears
      :param string_matrix: a data matrix: a list wrapping a list of strings, with each sublist being a sentence.
      :param character:
      :return:
      >>> word_for_char( [['the', 'quick', 'brown'],['how', 'now', 'cow']], 'n')
      ['brown', 'now']