Logical reasoning PrepTest 156 · Section 2 · Question 2

This doesn't weaken the argument. Still, this answer choice is a little tempting, as it suggests that large warm-blooded animals may not have a similar limb-to-core-body-temp ratio as the dinosaurs. However, we need to remember that the premises say that "dinosaurs had nearly the same body temperature in their limbs as in the rest of their bodies." The dinosaurs didn't necessarily have the exact same temperature in their limbs and the rest of their bodies. So, the evidence that large warm-blooded animals keep their "core body temperature slightly higher than the body temperature in their limbs" might be consistent with the premise about dinosaurs. Perhaps most dinosaurs also kept their core body temps slightly higher than their limb temps.

As we anticipated, this answer choice weakens the argument by showing that the dinosaur fossils are not reliable evidence of the temperature of dinosaurs' limbs or bodies. If the fossilization process alters the "original oxygen isotope ratios" in unpredictable ways, we really can't use those fossils to estimate the proportions of two oxygen isotopes. And if we can't estimate that proportion, we can't say that dinosaurs' limb-to-core-body-temp ratio is similar to that of warm-blooded animals. So, by undermining the author's key piece of evidence, this answer choice weakens the argument. And because this weakens the argument in a way that conforms to our anticipation, we can select it and give the remaining answers choices an, at most, quick check

This doesn't weaken the argument. We don't know whether oxygen being "more abundant in Earth's atmosphere" during the dinos' era would affect the proportion of the two oxygen isotopes in the dinosaurs' bones. Perhaps it did, but that's a major assumption we'd have to make to justify (C). Since we can't explain how (C) would weaken the argument without making this unjustified assumption, we need to eliminate it.

This answer choice doesn't weaken the argument. Still, it's a little tempting, as it tries to get us to think that large warm-blooded animals have a much different limb-to-core-body-temp ratio than dinosaurs. However, just because large warm-blooded animals have less uniform body temperatures than small warm-blooded animals doesn't mean that the temperatures of large warm-blooded animals' limbs are much lower than the rest of these animals' bodies. The temp of these animals' limbs could be only slightly lower than the rest of their bodies. And that's not necessarily inconsistent with the limb-to-core-body-temp ratio of dinosaurs, who had limbs that were "slightly" less warm than the rest of the bodies.

This doesn't weaken the argument. We don't care about how much oxygen warm-blooded animals use. We just care about the ratio of the oxygen isotopes in their bone. So, this answer choice is irrelevant to the argument.