DISCUSSION: This question says that the passage helps to answer the question asked by the right answer.
So you should narrow things down to 1-2 answers, then check that the passage actually does answer the question in the answer choice you choose.
- We don’t know what causes prions to replicate (last four lines of 4th paragraph), so it’s not clear whether blows to the head are relevant.
- Chronic insomnia is a symptom of CJD (second-to-last sentence of 2nd paragraph), but occasional insomnia isn’t mentioned as a symptom. Lots of people have occasional difficulty sleeping.
- Radiation or gene damage isn’t mentioned in the passage. Heck, prions don’t have genetic material. See the last sentence of 2nd paragraph, prions lack nucleic acid.
- The passage never says whether heredity is risk factor for CJD.
- CORRECT. The third-to-last sentence of 3rd paragraph shows that prions damage the brain by creating thread like structures.
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