【正确答案】 A

【答案解析】[听力原文]11-13 The most striking single fact about chimpanzees is the flexibility of their social life, the lack of any rigid form of organization. It represents about as far a departure from the baboon type of organization as one can find among the higher primates, and serves to emphasize the great variety of primate adaptations. Chimpanzees are more human than baboons, or rather they jibe better with the way we like to picture ourselves, as freewheeling individuals who tend to be unpredictable, do not take readily to any form of regimentation, and are frequently charming. (Charm is relatively rare among baboons.) Two researchers have described what they found during more than eight months spent among chimpanzees in their natural habitat, tide forest:" We were quite surprised to observe that there is no single distinct social unit in chimpanzee society. Not only is there no 'family' or 'harem' organization; neither is there a 'troop' organization-that is to say, no particular chimpanzees keep permanently together. On the contrary, individuals move about at will, alone or in Small groups best described as bands, which sometimes form into large aggregations. They leave their associates if they want to, and join up with new ones without conflict. " The general practice is best described as "easy come, easy go", although there are certain group-forming tendencies. As a rule chimpanzees move about in one of four types of band: adult makes only; mothers and offspring and occasionally a few other females; adults and adolescents of both sexes, but no mothers with young; and representatives of all categories mixed together. The composition of bands may change a number of times during the course of a day as individuals wander off and groups split or combine with other groups. On the other hand, certain individuals prefer one another's company. One of the researchers observed that four makes often roamed together over a four-month period, and mother often associated with their older offspring.