Which of the following examples represents the most remarkable demonstration of teaching animals to ...

Which of the following examples represents the most remarkable demonstration of teaching animals to communicate?
 
  a. Kanzi's mother, a chimp who learned to communicate through the pushing of geometric shapes on akeyboard
 b. Washoe the chimp who learned to combine signs into simple phrases
  c. Sarah the chimp who learned to communicate through placement of plastic chips d. A chimp named Nim Chimpsky learned to sign via operant conditioning
  e. Kanzi the chimp who learned to communicate through observation and imitation of his mother