Logical reasoning PrepTest 138 · Section 2 · Question 8

Incorrect. There's no discussion of a timeline for the depletion of the sediments, so this answer is unsupported—it might be quite some time before this happens.

Incorrect. This answer is too strong/extreme—the stimulus is about "certain" microbes, not "[e]very organism."

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Microbes eat shale, removing oxygen and generating CO2, which causes global warming, which causes the microbes to reproduce faster.

Answer Anticipation:
Much like conditional statements, causal statements can chain together. If petting a dog lowers blood pressure and lowered blood pressure decreases risk of heart disease, then petting a dog can contribute to decreased heart disease risk.

This stimulus presents a causal chain, starting with microbes eating shale and resulting in global warming, which causes the microbes to reproduce faster, which would lead to more CO2 being released, which results in more global warming, which . . .

So this causal chain reinforces itself, but the chain itself is what's important. The answer might deal with this "positive feedback loop," but any connection that's a part of the chain is supported and thus would be correct.

Answer Explanation:
The microbes release CO2, which promotes global warming, so their activity does exacerbate global warming. This answer is supported by our causal chain—in fact, it's supported by just one of the connections!

Key Takeaway:
Causal statements can chain together much as conditional ones do to form inferences. Additionally, Must Be True questions often have answers that don't utilize all of the statements in the stimulus, so don't fall for the trap of feeling the need to bring all of the statements together.

Incorrect. The stimulus doesn't mention any other elements that are removed from the atmosphere, but it never states that oxygen is the only element removed, so this answer is unsupported.

Incorrect. There's no discussion of the total amount of CO2 released, how much of it is made up of CO2 from microbes, or a comparison of the microbe-released CO2 to any other source, so this answer is out of scope.