PrepTest 109

Incorrect. The conclusion here is that one thing is "more likely" than another. That comparative conclusion doesn't match up with the If/OR structure of the conclusion in the stimulus so we can rule this answer choice out.

Incorrect. This argument is all over the place! However, if you skim it to the end, you can see the last sentence is the main point, and that doesn't match up with the If/OR structure of the stimulus. While that structure does show up in this answer, it's in a premise, so we can safely rule this out.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Valid

Question Type:
Parallel Reasoning

Stimulus Summary:
RT correct → not Object travel forward in time faster than light
QM — Tachyons travel faster than light
Conclusion — RT Correct → QM is wrong OR Tachyons travel backwards in time

Answer Anticipation:
This argument is complicated and scientific, but it also has some strong structural and logic—based keywords that we can use to work our way through it. Remember — this is a Parallel Reasoning question, so we should focus on those aspects in order to be able to quickly find a match!

The argument here starts with a conditional statement: If a given theory is correct, then something else is true. It then brings up another theory that brings up something that seems at odds with the first theory's implication. From that, it concludes that if the initial theory is correct, then either the second theory is wrong or the detail raised about it works out in a way that lines up with the first theory.

In other words, abstracting it, we get:
Theory A right → Implication
Theory B says something that seems to go against the implication
Conclusion — Theory A right → Theory B wrong OR Theory B's implication works in some way with Theory A

Don't worry too much about time travel and tachyons—instead, just know this overall structure!

Answer Explanation:
This answer's conclusion matches the If/OR structure of the stimulus, so let's diagram it out:
Modern medicine right → Human brain can't survive more than a few minutes without oxygen
Reliable witness — A shaman survived for a week buried underground
Conclusion — MM right → Witness is wrong OR Shaman had oxygen

While "Theory B" here is the word of a witness we don't need the exact content to match up just the logic. And here we have a theory (modern medicine) that makes a prediction a situation that seems to defy that prediction and then a conclusion conditioned on the first theory being right. That conclusion then says either the second viewpoint is wrong or the reality matches with the prediction made by the theory. This is a match for the stimulus so this is the correct answer.

Key Takeaway:
There's a lot of science in this stimulus but you could have ended up selecting the correct answer if you eschewed almost everything and focused only on the If/OR structure of the conclusion—only the correct answer was parallel in that way. Rely on these structural features when they're present in Parallel Reasoning questions! It's not a trick or a cheat—it's what these questions are about. Knowing the language that has logical relevance is the LSAT!

Incorrect. The conclusion here is that one thing is "more likely" than another so it doesn't match up with the conclusion in the stimulus.

Incorrect. First, this answer is inherently suspect because it is so topically similar to the stimulus—it's likely that it's designed to be a trap answer to get you to think you don't understand the science so you'll pick an answer that is as close as possible to the language of the stimulus. If you skimmed through the argument, you'd see a conclusion that settles on a single prediction of the future based on a theory, not an If/OR conclusion.