LSAT Question Stem

Which one of the following statements, if true, most seriously weakens the argument? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

This is a Weaken question type, which asks us to identify the statement that most seriously weakens the argument presented in the passage.

First, let's break down the argument:

Premise: Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills.

Premise: One possible cause is dioxin, which paper mills release daily and which can alter the concentration of hormones in fish.

Premise: However, dioxin is unlikely to be the cause, since the fish recover normal hormone concentrations relatively quickly during occasional mill shutdowns and dioxin decomposes very slowly in the environment.

Conclusion: Dioxin is unlikely to be the cause of the reproductive abnormalities in fish.

The argument's structure is based on the idea that dioxin is an unlikely cause for the reproductive abnormalities observed in fish downstream of paper mills because fish recover normal hormone levels quickly during mill shutdowns, despite dioxin decomposing slowly in the environment.

An "Evaluate" question for this argument could be, "Do the fish recover normal hormone concentrations during mill shutdowns due to a factor other than the absence of dioxin?"

Now, let's discuss each answer choice:

a) Some of the studies that show that fish recover quickly during shutdowns were funded by paper manufacturers.

This answer choice presents a source attack, which is logically invalid and does not undermine the argument.

b) The rate at which dioxin decomposes varies depending on the conditions to which it is exposed.

This answer choice does not provide concrete evidence to attack the argument. Although the rate of dioxin decomposition may vary, we do not know how it affects fish in their environment. Without specific information, this answer choice cannot weaken the argument.

c) Normal river currents carry the dioxin present in the river far downstream in a few hours.

This is the correct answer choice. If dioxin is quickly carried downstream by river currents, it becomes more likely that fish benefit from occasional shutdowns because their environment is temporarily free of dioxin. This makes dioxin a more likely culprit for the reproductive abnormalities, thus weakening the argument.

d) Some of the fish did not recover rapidly from the physiological changes that were induced by the changes in hormone concentrations.

While this answer choice might seem to weaken the argument by suggesting that reproductive abnormalities could persist in dioxin-exposed fish despite hormonal adjustments, it does not directly address the reason given in the argument for why dioxin is unlikely to be the cause. Therefore, it does not effectively weaken the argument.

e) The connection between hormone concentrations and reproductive abnormalities is not thoroughly understood.

This answer choice does not weaken the argument, as the lack of understanding about the connection between hormone concentrations and reproductive abnormalities does not suggest that the relationship is either stronger or weaker than previously believed. Without concrete information, this answer choice cannot attack the argument.