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11.为什么D正确，E错误 12， 完全没有思路， 两个否定not, free, 我就晕了， 哪位大侠帮忙解释，OG的解释没有理解 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 fractures
in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea
tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than
those in the present-day species.
In considering possible explanations for this finding, the researchers dismissed demographic bias
because older individuals were not overrepresented in the fossil samples. They rejected
preservational bias because a total absence of breakage in two extinct species demonstrated that
the fractures were not the result of abrasion within the pits. They ruled out local bias because
breakage data obtained from other Pleistocene sites were similar to the La Brea data. The
explanation they consider most plausible is behavioral differences between extinct and present-day
carnivores-in particular, more contact between the teeth of predators and the bones of prey due to
more thorough consumption of carcasses by the extinct species. Such thorough carcass
consumption implies to the researchers either that prey availability was low, at least seasonally, or
that there was intense competition over kills and a high rate of carcass theft due to relatively high
predator densities.
11. The researchers’ conclusion concerning the absence of demographic bias would be most
seriously undermined if it were found that
(A) the older as individual carnivore is, the more likely it is to have a large number of tooth
fratures
(B) the average age at death of a present-day carnivores is greater than was the average age
at death of a Pleistocene carnivore
(C) in Pleistocene carnivore species, older individuals consumed carcasses as thoroughly as
idd younger individuals
(D) the methods used to determine animals’ ages in fossile samples tend to misidentify many
older individuals as younger individuals
(E) data concerning the ages of fossil samples cannot provide reliable information about
behavioral differences between extinct carnivores and present-day carnivores the researchers dismissed demographic bias
because older individuals were not overrepresented in the fossil samples"研究人员排除人口统计的偏见，因为老年在化石的样品中没有过多的代表，那么可以推出，越是化石显示老年越能推出后面的结论“that prey availability was low, at least seasonally, or
that there was intense competition over kills and a high rate of carcass theft due to relatively high
predator densities.” 研究人员排除人口统计的偏见，因为老年在化石的样品中没有过多的代表，那么可以推出，越是化石显示老年越能推出后面的结论“that prey availability was low, at least seasonally, or
that there was intense competition over kills and a high rate of carcass theft due to relatively high
predator densities.” A，越老的predator, tooth 就磨损越严重，就越能推出后面的结论”that prey availability was low, at least seasonally, or
that there was intense competition over kills and a high rate of carcass theft due to relatively high
predator densities“， 显然A是支持，没有削弱 可以显然排除B， 文中就没有平均年龄的问题 在排除C，文中没有提到younger 与thorough的问题 D，判断年龄的方法错误地把80岁当成30岁（比如），为什么就削弱结论呢？ E，难道”data concerning the ages of fossil samples cannot provide reliable information about
behavioral differences between extinct carnivores and present-day carnivores“ 不是削弱吗？ 根据化石上的年龄判断不能提供结论，这不是削弱了结论吗，显然是否定前提，
12. The passage suggests that if the researchers had not found that two extinct carnivore species
were free of tooth breakage, the researchers would have concluded that
(A) the difference in breakage frequencies could have been the result of damage to the fossile
remains in the La Brea pits
(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the
fossils in the La Brea pits
(C) Pleistocene carnivore species probably behaved very similarly to one another with respect
to consumption of carcass
(D) all Pleistocene carnivores species differed behaviorally from present-day carnivore
species.
(E) predator desities during the Pleistocene era were extremely high
12. The passage suggests that if the researchers had not found that two extinct carnivore species
were free of tooth breakage, the researchers would have concluded that
(A) the difference in breakage frequencies could have been the result of damage to the fossile
remains in the La Brea pits
(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the
fossils in the La Brea pits
(C) Pleistocene carnivore species probably behaved very similarly to one another with respect
to consumption of carcass
(D) all Pleistocene carnivores species differed behaviorally from present-day carnivore
species.
(E) predator desities during the Pleistocene era were extremely high
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