Which statement best sums up the linguistic ability of nonhuman animals?
a. Nonhuman animals that are taught sign language are nearly as competent as humans in terms of combining vocabulary into creative sentences.
b. Some animals, such as chimpanzees, have had success imitating human speech sounds and speaking many vocabulary words in isolation, but they can't string sentences.
c. It is clear that many animals can learn vocabulary from human languages, and can combine a couple of signs together, but they do not have complex grammar.
d. More intelligent animals can learn to repeat full sentences of spoken human language, but there is no evidence that they actually know the meanings of any of