托福阅读：SOCIAL BEHAVIOR

　Social behavior is #munication that permits a group of animals ofthe same species to be#e organized cooperatively. Social behavior includes any interaction that is a　consequence of one animal's response to another ofits own species, such as an individual fighting to defend a territory. However, not all aggregations of animals are social. Clusters of moths attracted to a light at night or trout gathering in the coolest pool of a stream are groupings of animals responding to environmental signals. Social aggregations, on the other hand, depend on signals from the animals themselves, which stay together and do things together by influencing one another.

　　Social animals are not all social to the same degree. Some species cooperate only long enough to achieve reproduction, while others-such as geese and beavers-form strong pair bonds that last a lifetime. The most persistent social bonds usually form between mothers and their young. For birds and mammals, these bonds usually end when the young can fly, swim, or run, and find enough food to support themselves.

　　One obvious benefit of social organization is defense-both passive and active-from predators. Musk oxen that form a passive defensive circle when threatened by a pack of wolves are much less vulnerable than an individual facing the wolves alone. A breeding colony of gulls practices active defense when they, alerted by the alarm calls of a few, attack　a predator as a group. Such a collective attack will discourage a predator more effectively than individual attacks. Members of a town of prairie dogs cooperate by warning each other with a special bark when a predator is nearby. Thus, every individual in a social organization benefits from the eyes, ears, and noses of afl other members ofthe group. Other advantages of social organization include cooperation in hunting for food, hu&:Hing for protection from severe weather, and the potential for transmitting information that is useful to the society.

　　Why does the author mention moths and trout in paragraph l?

　　A. To show how social behavior benefits each individual in a group

　　B. To pomt out the role of the environment in social organization

　　C. To give examples of groupings that do　not represent social behavior

　　D.To explain how not all social behavior has the same purpose