What Have We Learned from Studies in Which Researchers Have

What have we learned from studies in which researchers have attempted to teach chimpanzees and bonobos to use nonverbal language (i.e.,sign language or communication boards)

A)  Some have appeared to learn many words and have combined words in appropriate ways. 
B)  They are capable of learning language to a level equivalent to that seen in 10-year-old children. 
C)  They are not capable of acquiring nonverbal communication. 
D)  They can use nonverbal methods to communicate with other primates, but not with humans.