06年GRE模拟试题第3部分
文章作者 100test 发表时间 2007:02:25 20:09:21
来源 100Test.Com百考试题网
One explanation for the tendency of animals to be more vigilant in smaller groups than in larger ones assumes that the vigilant behavior-looking up， for example-is aimed at predators. If individuals on the
（5） edge of a group are more vigilant because they are at greater risk of being captured， then individuals on aver- age would have to be more vigilant in smaller groups， because the animals on the periphery of a group form a greater proportion of the whole group as the size of the
（10）group diminishes. However， a different explanation is necessary in cases where the vigilant behavior is not directed at predators. J. Krebs has discovered that great blue herons look up more often when in smaller flocks than when in larger
（15）ones， solely as a consequence of poor feeding conditions. Krebs hypothesizes that the herons in smaller flocks are watching for herons that they might follow to better feeding pools， which usually attract larger numbers of the birds.
17.It can be inferred from the passage that in species in which vigilant behavior is directed at predators， the tendency of the animals to be more vigilant in smaller groups than in larger ones would most likely be minimized if which of the following were true？
（A） The vigilance of animals on the periphery of a group always exceeded that of animals located in its interior， even when predators were no in the area.
（B） The risk of capture for individuals in a group was the same， whether they were located in the interior of the group or on its periphery.
（C） Animals on the periphery of a group tended to be less capable of defending themselves from attack by predators than animals located in the interior of the group.
（D） Animals on the periphery of a group tended t bear marks that were more distinctive to predators than animals located in the interior of the group.
（E） Animals on the periphery of a group tended to have shorter life spans than animals located in the interior of the group.