Until recently, scientists did not know of a close vertebrate analogue to th

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问题 Until recently, scientists did not know of a close vertebrate analogue to the extreme form of altruism observed in eusocial insects like ants and bees, whereby individuals cooperate, sometimes even sacrificing their own opportunities to survive and reproduce, for the good of others. However, such a vertebrate society may exist among un- der ground colonies of the highly social rodent Heterocephalus glaber, the naked mole rat.
A naked mole rat colony, like a beehive, wasp s nest, or termite mound, is ruled by its queen, or reproducing female. Other adult female mole rats neither ovulate nor breed. The queen is the largest member of the colony, and she maintains her breeding status through a mixture of behavioral and, presumably, chemical control. Queens have been long-lived in captivity, and when they die or are removed from a colony one sees violent fighting for breeding status among the larger remaining females, leading to a takeover by a new queen.
Eusocial insect societies have rigid caste systems, each insects’ s role being defined by its behavior, body shape, and physiology. In naked mole rat societies, on the other hand, differences in behavior are related primarily to reproductive status(reproduction being limit- ed to the queen and a few males), body size, and perhaps age. Smaller non-breeding members, both male and female, seem to participate primarily in gathering food, transporting nest mate- rial, and tunneling. Larger nonreaders are active in defending the colony and perhaps in removing dirt from the tunnels. Jarvis’ work has suggested that differences in growth rates may influ- ence the length of time that an individual performs a task, regardless of its age. Cooperative breeding has evolved many times in vertebrates, but unlike naked mole rats, most cooperatively breeding vertebrates(except the wild dog, Lycaon pictus)are dominated by a pair of breeders rather than by a single breeding female. The division of labor within social groups is leas pronounced among other vertebrates than among naked mole rats, colony size is much smaller, and mating by subordinate females may not be totally suppressed, whereas in naked mole rat colonies sub- ordinate females are not sexually active, and many never breed. [br] One function of the third paragraph of the passage is to

选项 A、state a conclusion about facts presented in an earlier paragraph.
B、introduce information that is contradicted by information in the fourth paragraph.
C、qualify the extent to which two previously mentioned groups might be similar.
D、show the chain of reasoning that led to the conclusions of a specific study.
E、demonstrate that, of three explanatory factors offered, two may be of equal significance.

答案 C

解析第三段职能：A．做结论。无。B．给出和第四段相反信息。三、四两段不是相对立的。C．正确。限制前面说的两类群体相似程度。前已指出裸鼹鼠和社会性质昆虫具有类似的利他主义，这一段讲两者的区别。D．“show the chain of reasoning”无。E．指出三种因素中，两种同等重要。无。

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