Logical reasoning PrepTest 135 · Section 2 · Question 23

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Bacteria that would die if exposed to oxygen produce hydrogen sulfide that:
(1) Protects it from oxygen/removes oxygen
(2) Tends to kill other organisms, making food
This bacteria thus creates an environment where it can survive FOREVER.

Answer Anticipation:
Yes, all caps. That word at the end—"indefinitely"—is unbelievably strong, and thus it's likely to play into the correct answer. Remember, though, that this is a Must Be True question, so we have to accept that it's true that these bacteria can create an environment that will allow them to thrive indefinitely.

Since this statement is noted as being "as a result" of the production of hydrogen sulfide, it must be the case that that process can continue indefinitely, protecting the bacteria from oxygen and providing it with food.

Other than that, it's hard to see what specific correct answer might be provided, so let's head to the answers and work through them based on our understanding of the passage.

Answer Explanation:
This answer matches our anticipation, and it relies on the strong statement at the end and the note that it's a "result of" the production of hydrogen sulfide. If the indefinite lifespan of the bacterial colony is a result of the production of hydrogen sulfide, it must be able to do so indefinitely.

Key Takeaway:
When you're in a Must Be True stimulus with complex and hard-to-understand subject matter, focus on the elements that tend to lead to correct answers—conditionals, causal relationships, comparisons, and strong statements.

Incorrect. While hydrogen sulfide reacts with and removes oxygen, and kills other organisms, there's no statement that links those two processes as being causally related. The hydrogen sulfide could be poisonous itself.

Incorrect. The argument supports that enough organisms to feed the bacterial colony die when exposed to hydrogen sulfide, but that doesn't mean that "most" organisms exposed to the chemical will provide food if killed by the chemical.

Incorrect. Two issues with strength here. First, there's no indication that the bacteria can continue to survive "only" in such an environment—there may be other areas where the conditions are met without the hydrogen sulfide being involved. Second, there's no indication that "all" oxygen needs to be removed from the environment—just enough that it doesn't come into contact with enough of the bacteria to kill off the colony.

Incorrect. This answer is too strong in saying that "any" bacterial colony that produces this chemical can see the benefits since the stimulus is about only "certain bacteria that produce hydrogen sulfide," not all bacteria that do so.