challenge: According to Anna Maria Di Sciullo and Edwin S. Williams in 'On the Definition of Word,' what are the four concepts they distinguish as types of 'word'?
  
  A. semantemes, phonetic units, syntactic structures, morphological units
  B. syntactic atoms, listemes, phonetic units, morphological objects
  C. listemes, morphological objects, syntactic atoms, phonological words
  D. phonological words, semantemes, syntactic structures, morphological units
  Answer: 