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  3. A recent study has provided clues to predator-prey dynamics in the late Pleistocene era.Researchers compared the number of tooth

A recent study has provided clues to predator-prey dynamics in the late Pleistocene era.Researchers compared the number of tooth

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问题     A recent study has provided clues to predator-prey dynamics in the late Pleistocene era.Researchers compared the number of tooth fractures in present-day carnivores with tooth fracturesin carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Breatar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher thanthose in the present-day species.
    In considering possible explanations for this finding, the researchers dismissed demographic biasbecause older individuals were not overrepresented in the fossil samples. They rejectedpreservational bias because a total absence of breakage in two extinct species demonstrated thatthe fractures were not the result of abrasion within the pits. They ruled out local bias becausebreakage data obtained from other Pleistocene sites were similar to the La Brea data. Theexplanation they consider most plausible is behavioral differences between extinct and present-daycarnivores-in particular, more contact between the teeth of predators and the bones of prey due tomore thorough consumption of carcasses by the extinct species. Such thorough carcassconsumption implies to the researchers either that prey availability was low, at least seasonally, orthat there was intense competition over kills and a high rate of carcass theft due to relatively highpredator densities.
选项 A、present several explanations for a well-known fact
B、suggest alternative method of resolving a debate
C、argue in favor of a controversial theory
D、question the methodology used in a study
E、discuss the implications of a research finding
答案E
解析 This question asks you to identify the primary purpose of the passage. Choice E is the best answer. The first paragraph of the passage mentions evidence discovered at the Rancho La Brea tar pits and suggests that his evidence provides information about predator-prey dynamics in the late Pleistocene era. After dismissing possible alternative explanations, the second paragraph describes what is considered to be the most likely explanation for the findings. Choice A is incorrect because the passage discusses several explanations for the findings but only in order to eliminate them as rivals of the explanation that credits behavioral difference. In addition, there is no indication of how well known the evidence regarding tooth fractures is. Choice B is incorrect because no alternative methods for resolving a debate are mentioned. Choice C is incorrect because there is no suggestion in the passage that the preferred explanation for the tooth factures is controversial. Choice D is incorrect: there is nothing in the passage to suggest that the evidence discussed in the passage or the way in which it is analyzed its questionable.
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