Section B
Directions: There are 2 passages in this section．Each passage is followed by some questions or unfinished statements．For each of them there are four choices marked A, B, C and D．You should decide on the best choice.
Allelomimetic behavior．may be defined as behavior．in which two or more individual animals do the same thing, with some degree of mutual simulation and coordination．It can only involve in species with sense organs that are well enough developed so that continuous sensory contact can be maintained．It is found primarily in vertebrates(脊椎动物), in those species that are diurnal, and usually in those that spend much of their lives in the air, in open water or on open plains.
In birds, allelomimetic behavior．is the rule rather than the exception, though it may occasionally be limited to particular seasons of the year as it is in the red wing blackbird．Its principal function is that of providing safety from predators(掠食者), partly because the flock can rely on many pairs of eyes to watch for enemies, and partly because if one bird reacts to er, the whole flock is warned.
Among mammals, allelomimetic behavior．is very rare in rodents(啮齿动物), which almost never move in flocks or herds．Even when they are artificially crowded together, they do not conform．in their movements．On the other hand, such behavior．is a major system among large-hoofed mammals, such as sheep.
In the pack-hunting carnivores(食肉类飞禽),allelomimetic behavior．has another function of cooperative hunting for large prey(被捕食者) animals, such as moose．Wolves also defend their dens as a group against larger predators, such as bears.
Finally, allelomimetic behavior．is highly developed among most primate groups, where it has the principal function of providing warning against predators, as though combined defensive behavior．is also seen in troops of baboons(狒狒).
The main topic of the passage is the ______.