LR Question 10 Explanation
QUESTION TEXT: A recent study suggests that Alzheimer’s disease…
QUESTION TYPE: Strengthen
CONCLUSION: Alzheimer’s may be caused by a virus.
REASONING: Blood from Alzheimer’s patients was injected into rats. The rats developed symptoms of Creutzfeld-Jacob disease, another degenerative neurological disorder. Creutzfeld-Jacob disease is caused by a virus.
ANALYSIS: The fact that the rats got sick implies that something in the human blood (perhaps a virus) caused them to get sick. But they got a different disease.
This doesn’t help show that Alzheimer’s is caused by a virus unless the two diseases are related. Answer choice D says they are the same disease.
___________
- This would weaken the argument that Alzheimer’s is caused by a virus in humans.
- It doesn’t really matter what the symptoms are. The main point is that the disease is caused by a degeneration of brain tissue, just like Alzheimer’s.
- This also weakens the argument. We’d like to think that the disease is caused by a virus in both species.
- CORRECT. If the diseases aren’t the same then it isn’t clear how rats getting Creutzfeld-Jacob disease shows that Alzheimer’s is caused by a virus. Just because the diseases are both neurological disorders, that doesn’t mean they have the same causes.
- This doesn’t help much, because the sick rats were injected with human blood, not rat blood.
More Resources for Strengthen Questions
- Intro Course lesson: This intro course lesson covers Strengthen questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers strengthen questions.
I understand why (D) is correct but still not clear to eliminate (E)
(E) Blood from rats without Creutzfeldt-Jakob disease produced no symptoms of the disease when injected into other experimental rats.
Study is that blood was taken from humans and injected into rats, blood should have virus which caused that Creutzfeldt disease in rats.
Now, option (E) implicitly says that blood from rats without Creutzfeldt didn’t have any virus, doesn’t this increase our confidence in the conclusion by eliminating another alternate cause of virus presence? Had virus been already present in blood of these rats before injecting into them from humans then it would have weakened the conclusion that blood of humans had virus and caused the disease.
Please let me know what I am thinking wrong here.
E talks about blood from rates with Creutzfeldt-Jakob disease being injected into other rats and not causing any symptoms. This might seem to rule out the possibility that the rats somehow already had the disease or were spreading it to each other. But that’s not actually relevant to the core question. The point of the study is the initial human-to-rat transmission. Whether rats can infect other rats with C-J doesn’t tell us anything about whether HUMAN blood contained a virus, or whether that virus is connected to Alzheimer’s.
If anything, E introduces a confusing variable: if a virus caused the disease in the first rats, why wouldn’t it be transmissible? So rather than strengthening the hypothesis, E raises more questions than it answers but most importantly doesn’t provide meaningful support for the idea that Alzheimer’s is caused by a virus.
Thanks for your response.
I think I realise my mistake now. I was thinking that virus (whether it is present in rats or humans) is causing Alzheimer’s but it seems like the argument was concerned about virus present in HUMANS only. Do you also agree that this led me to select option E? If this is true then I am convinced why I didn’t select option D.