Recent research on communications with gorillas and chimpanzees suggest that these animals can learn ...

Recent research on communications with gorillas and chimpanzees suggest that these animals can learn to use language. The conclusion that these animals truly use language has been criticized because .
 
  a. gestures and other simple responses can be learned through conditioning and reinforcement without a true use of language
  b. language is a uniquely human attribute that cannot be shared with animals
  c. the language abilities of chimpanzees are too limited to represent any form of language d. phonemes cannot be used by chimpanzees or other animals
  e. researchers have not agreed on an adequate definition of language