大全106－235

Passage 106 (6/17)

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 (something killed) and a high rate of carcass theft due to relatively high predator densities.

235. 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 fossil 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（A）

(E) predator densities during the Pleistocene era were extremely high

为什么是A？