Passage 1 
Some years ago, Winthrop and Luella Kellogg decided to study this and other questions, rearing a chimpanzee (黑猩猩) in a normal human environment, Gua, a seven-and one-half-month-old female chimpanzee, was adopted into their household to be treated in the same fashion as their ten-month-old son Donald. The two babies were dressed alike, fed in the same way, and allowed equal play opportunities. In going to the park, going to bed, or being toilet trained, both had essentially similar experiences, and the parents tried to give them equal love. 
Shortly after the experiment began, Gua became slightly superior to Donald in word recognition, but Donald's inferiority (劣势) might be explained on the basis of less physical ability. The chimpanzee was more agile (灵活 ) and therefore could respond more readily to such requests as "Get up on the chair." As time passed, however, the child gained rapidly on the chimpanzee, and by the end of the period of investigation he was significantly ahead in word recognition. 
In word usage, Gua remained nonverbal (不以言语表达 ) throughout the experiment. Her communications included some gestures, such as wriggling (努力) her lips when she wanted apples but no words. She only gave sudden barks or cries in moments of excitement, fear, or pain. Donald, on the other hand, passed through the normal stages in learning a spoken language and, by the end of the research, uttered his first words. He said "da" meaning "down" and "bowwow for the dog, and he used a few other words." But as his parents emphasized, he had not shown language mastery (掌握) either. At the end of the study, he still had not used words in combination. Unfortunately, this research had to be discontinued after nine months partly because of the increasing strength and enormous agility (灵活，敏捷) of Gua around the house. 

21. The main idea of this passage is ___________. 
 A. to show how chimpanzees talk 
 B. to describe the experiment on language learning 
 C. to show the problems children have in communicating among themselves