Summarize Argument
Dinosaurs were likely warm-blooded because the oxygen isotopes in their bones suggest that their limbs had the same body temperature as the rest of their body. And typically, the body temperature of modern cold-blooded animals much is higher than their limbs.
Notable Assumptions
The author assumes that the discrepancy in the body/limb temperature of modern cold-blooded animals was the same as cold-blooded animals during the time of the dinosaurs. The author also assumes that the process of determining body temperature from bones is applicable to dinosaur fossils.
A
Large warm-blooded animals keep their core body temperature slightly higher than the body temperature in their limbs.
This does not weaken because dinosaurs' core body and limb temperature are still much closer to the ratio of warm-blooded animals. Thus, this does not weaken the claim that dinosaurs were warm-blooded.
B
The fossilization process introduces changes to bones such that their original oxygen isotope ratios cannot be predicted.
This weakens the argument because it casts doubt on the process by which the evidence was discovered. If the fossilization process changes the oxygen distribution, then the evidence about the body temperature cannot be relied on to reach a sound conclusion.
C
Oxygen was more abundant in Earth’s atmosphere during the period in which the dinosaurs lived.
You must make several unwarranted assumptions to make this work. The fact that more oxygen was prevalent in the atmosphere does not mean dinosaur bones have more oxygen. AC B does a much better job of weakening the process of how the evidence was collected.
D
Small warm-blooded animals like mice tend to have more uniform body temperatures than do large warm-blooded animals like elephants.
This does not weaken the argument that dinosaurs are warm-blooded. This AC just compares small and large warm-blooded animals. You have to make many unwarranted assumptions for this to work.
E
Warm-blooded animals are more active and use more oxygen than cold-blooded animals.
This is irrelevant to the argument’s reasoning. This just provides a characteristic of warm-blooded animals but does not challenge the evidence or reasoning in the stimulus.
"Surprising" Phenomenon
Why are small rats more likely than normal rats to suffer from heart problems, and large rats are less likely than normal to suffer form heart problems?
Objective
This is an EXCEPT question. The four wrong answers will help differentiate small rats from other rats in a way that makes them more likely to have heart problems, or it will help differentiate large rats from other rats in a way that makes them less likely to have heart problems.
A
Small rats are more likely than large rats to suffer from fatal diseases that tend to strike earlier than do heart problems.
This deepens our confusion. If small rats are more likely than large rats to die before getting heart problems, then we’d expect the overall rate of heart problems among small rats to be lower than for the other rats, who are more likely to survive to the age of getting heart problems.
B
Small rats generally have smaller blood vessels than do large rats, vessels that can more easily be clogged with fatty deposits.
If small rats have smaller blood vessels, which can be more easily clogged with fat, that’s a potential causal mechanism that could explain the smaller rats’ increased risk of heart problems.
C
The larger a rat is, the more successful it will be at defending itself, and therefore the less stressful its existence will be.
The smaller ones have more stress, which might lead to increased heart problems. The larger rats have less stress, which might lead to fewer heart problems. And the average rats are in the middle for stress, which might lead to being in the middle for heart problems.
D
In addition to being the leading cause of weak hearts in adult rats, malnutrition at early stages of development causes rats to be undersized.
This tells us malnutrition causes both a weak heart and smaller body size. This could explain why the smaller rats have more heart problems: those rats were more likely to be the malnourished ones.
E
Although large rats are no more active than rats of average size, they tend to be much more active than small rats, resulting in greater cardiovascular conditioning.
(E) establishes that small rats have less cardiovascular conditioning (meaning conditioning related to the heart) than the average and large rats. This helps explain why small rats have more heart problems than the other groups.