Research in Which Chimpanzees Are Trained to Use Language Reveals

Research in which chimpanzees are trained to use language reveals all of the following except that

A) chimpanzees can be taught to communicate using gestures.
B) chimpanzees can communicate using plastic chips as words.
C) chimpanzees cannot master anything beyond the simplest of grammatical rules.
D) acquisition of language by humans need not involve any innate mechanisms.