原文：
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 Breatar
pits in Los Angeles. The breakagefrequencies in the extinct species were strikingly higher than those in the present-day species.（指出研究后的发现）
In considering possible explanations for this finding,
（文章开始讨论对研究发现的解释）the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. （排除了统计差异）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.
（排除了保存差异）They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data.
（排除了地域差异）The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores（给出解释：行为差异）—in particular（开始进一步阐述）, 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.
题目（第7题）
The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that
(A) the older an individual carnivore is, the more likely it is to have a large number of tooth fractures
(B) the average age at death of a present-day carnivore 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 did younger individuals
(D) the methods used to determine animals’ ages in fossil 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
答案：D
OG解释：
Begin by looking at the section on demographic bias. Lines 11–13 state that demographic bias has been ruled out as an explanation because“older individuals were not overrepresented in the fossil samples”. This implies that older carnivores would be expected to have more tooth fractures than younger ones. To answer this question, read each answer choice to find the one statement that undermines the researchers’ conclusion. If the method to determine age in the fossil samples is faulty and older carnivores are misidentified as younger ones, then demographic bias cannot be dismissed.
我的问题是：上述红色字体的结论是怎么推出来的？为什么older individuals没有占到过大的比例就说明他们会有更多的tooth fractures呢？在解释A选项时，为什么OG直接认为“This statement supports rather than undermines the researchers’ conclusion”呢？
谢谢！
| 
