Logical ReasoningDifficulty: Hard

PT141 S4 Q8 Explanation

Fluoride enters a region's groundwater

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Stimulus

Fluoride enters a region's groundwater when rain dissolves fluoride-bearing minerals in the soil. In a recent study, researchers found that when rainfall, concentrations of fluoride-bearing minerals, and other relevant variables are held constant, fluoride concentrations in groundwater are also contains a high concentration of sodium.

What this question is testing

Most Supported

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
8.

Which one of the following can most reasonably be concluded on the basis of

Answer choices

  1. Too Specific: primary7% picked this

    Fluoride-bearing minerals are not the primary source of fluoride found

    We have no idea how many sources of fluoride there are, and which one is or isn't the primary source. This paragraph never compares sources of fluoride. This answer is probably trying to get people to think that the paragraph is saying that sodium is the primary source of fluoride, but sodium isn't even identified as a source of fluoride.

  2. Contradicted4% picked this

    Rainfall does not affect fluoride concentrations

    The first sentence says that rain can lead directly to fluoride entering the groundwater.

  3. Unknown Comparison: dissolve faster3% picked this

    Sodium-bearing minerals dissolve at a faster rate than

    Nothing in this paragraph deals with comparative degrees of dissolving. We couldn't possibly divulge which element is a faster dissolver form this paragraph.

  4. Correct55% picked this

    Sodium in groundwater increases the rate at which fluoride-bearing

    Why this is right

    This, of course, is not a must be true, but this is one of the possible interpretations of the correlation in the final sentence. Given that rain + FL-bearing minerals = FL in groundwater and given that when you control for amount of rain and amount of FL-bearing minerals, the fluoride seems to make it into the groundwater at significantly higher rates when there is sodium present, it seems like the sodium does something to facilitate higher fluoride concentration. This answer is offering a plausible guess, based on the fact that when all other relevant variables are controlled for, higher sodium seems to mean higher fluoride in the groundwater.

    Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.

  5. Out of Scope: sodium-bearing minerals32% picked this

    Soil that contains high concentrations of sodium-bearing minerals also contains high concentrations

    We only talk about certain groundwater having lots of sodium. We don't have any information about soil with lots of sodium-bearing minerals.

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