21. The video shows chimpanzees using sign language to talk to one another, people and..
22. Since the videos appear dated, a student questions whether scientists currently perform similar .............
23. The professor admits that the examples in the videos are.. ones.
24. A student did not expect that chimpanzees would bet so.. with human language.
25. Recent research found that chimpanzees used sign language to communicate in the..
26. It is mentioned that the way people control their vocal cords, .., teeth and lips is unique to humans.
27. The use of a voice is not a.. in all human languages.
28. Unless they are.. by humans, Chimpanzee sign language is very simple.