PrepTest 111, Section 4, Question 10
A recent study suggests that Alzheimer's disease, which(64 more words not shown)
Which one of the following(17 more words not shown)
- AAlzheimer's disease in(7 more words not shown)
- BCreutzfeldt-Jakob disease affects(9 more words not shown)
- CThe virus that(10 more words not shown)
- DThe symptoms known,(14 more words not shown)
- EBlood from rats(15 more words not shown)
Reading the argument
The rats developed symptoms of a different disorder. How does that establish anything about what causes Alzheimer's disease?
The study starts with blood from eleven people with Alzheimer's. I'd want to know how representative those volunteers were, but the number alone doesn't tell us the study is worthless. The more immediate puzzle is the connection between the two diseases: after receiving the blood, the rats show symptoms associated with Creutzfeldt-Jakob disease, not simply the original human diagnosis.
The passage tells us that Creutzfeldt-Jakob disease is caused by a virus. Let's use that fact as given here. We still need to connect it to the hypothesis about Alzheimer's. Merely naming two degenerative disorders doesn't establish that they have the same cause.
What we’re looking for
We're asked to strengthen the scientist's hypothesis. I'd look for evidence tying the result in the rats to the disease in the human volunteers. Some connection between the disorders and their causes would help explain why this study supports the possibility the scientist proposes.
Working the answers
- A
A nonviral cause of Alzheimer's in rats wouldn't support a viral cause in humans. It might raise another question about comparing the animals and people, but it doesn't supply the connection this argument needs. The answer points away from a viral explanation in the animals rather than toward one.
- B
This emphasizes a difference: one condition would affect the rats' limb nerves while the human disease attacks the brain. That doesn't help connect the rat result to the proposed human cause. A stronger link between the conditions would be useful; a newly specified difference doesn't provide it.
- C
If the virus responsible for the rats' disease has no effect on humans, identifying it in the rat outcome would give us less reason to think it explains the human illness. C doesn't establish that no virus could cause Alzheimer's, but it doesn't strengthen the particular connection the study is being used to suggest.
- DCorrect
This supplies a much stronger connection: the two sets of symptoms are different manifestations of the same disease. Now the virus-caused condition described in the rats isn't merely some unrelated neurological disorder. It is another form of the disease associated with the human symptoms.
Using the passage's statement about the viral cause, that common identity strongly supports the proposed viral explanation of Alzheimer's. The different names and symptoms had made the leap puzzling; D explains why the rat result bears on the human disease.
- E
This describes another injection involving rats without Creutzfeldt-Jakob disease. The absence of symptoms afterward might help us ask whether an injection alone produces symptoms, but it doesn't explain the connection between Alzheimer's in the human donors and the different symptoms in the original rats. D supplies that disease connection directly; E leaves it missing.
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