Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One possible...

Skylar on March 1, 2020

@oliveds,

Weaken questions can be hard to grasp at first. You are correct that the right answer will weaken the argument, but more specifically it will weaken the conclusion of the argument. It can do this in a variety of ways, including by showing that the conclusion does not necessarily follow, providing an alternate cause, showing cause without effect or effect without cause, showing that a cause-effect relationship is backwards, showing that correlation was mistaken for causation (so naming something else that caused both things), and showing a Sufficient condition without the Necessary condition. If an answer is irrelevant or leaves you room to ask "okay sure, but why does this matter?" it is typically incorrect. The best way to grasp these concepts is to do practice problems and take the time to thoroughly review both why the correct answer was correct and why the incorrect answers were incorrect.

In terms of this specific question, I wrote a full explanation in response to your other post. Basically though, the correct answer highlights the fact that the passage's conclusion does not necessarily follow from the passage's premises by offering a new explanation for those premises. I have attached my explanation below for your convenience:

First, let's break down the passage:
P: Fish immediately downstream of paper mills have reproductive abnormalities.
P: One possible cause of these abnormalities is dioxin- which is released from paper mills and can alter fish hormone concentrations.
P: The fish recover normal hormone concentrations relatively quickly during mill shutdowns.
P: Dioxin composes very slowly in the environment.
C: So, Dioxin is unlikely to be the cause.

This is a Weaken question. So we are looking for the answer choice that will weaken the passage's conclusion- which is that dioxin is unlikely to be the cause for the reproductive abnormalities in the fish.

It is important to understand the reasoning that the passage offers in support of this conclusion- which is that the fish recover normal hormone concentrations relatively quickly during mill shutdowns and dioxin composes very slowly in the environment. In other words, since dioxin is present in the environment for a long time and the fish immediately downstream of paper mills recover quickly when the mills are shut down, the passage concludes that dioxin is not likely the cause of the abnormalities. This is because, if dioxin was the cause, we would not expect the fish to recover immediately since the dioxin would still be lingering in the environment. Understanding this is key to completing this question.

Now, let's turn towards the answer choices.

(A) discusses the funding of the study. This answer choice is trying to trick students into making the assumption that the study was biased because it was paid for by paper manufacturers. However, equating the finding source with bias requires an assumption that is not explicitly supported by the passage, so (A) does not weaken the passage and is incorrect.

(B) notes that the rate of dioxin decomposition varies depending on conditions. We already know from the passage that dioxin "decomposes very slowly," so any minor variance in this rate due to conditions is irrelevant. Whether the dioxin decomposes very slowly as opposed to extremely slowly has no effect on the passage's reasoning, so (B) does not weaken the passage and is incorrect.

(C) states that "normal river currents carry the dioxin present in the river far downstream in a few hours." This means that the dioxin passes the fish who are immediately downstream from the paper mills quickly. This would allow the fish to be impacted by the dioxin as it passes them, but, when the mill shuts down, to recover quickly because the dioxin is downstream. In turn, the dioxin can take a long time to decompose downstream without affecting the fish immediately near the paper mills. Therefore, this answer choice shows that dioxin could still be the cause of reproductive abnormalities in the fish by offering a new explanation for the premises that the passage used to reach its conclusion. So, (C) weakens the passage and is correct.

(D) discusses "some" of the fish. "Some" means "at least one, possibly all," and since the specific amount it refers to here is left unspecified, we cannot be sure of its full impact. More importantly though, (D) refers to "physiological changes that were induced by the changes in hormone concentrations," whereas the passage is only concerned specifically with the reproductive abnormalities. Therefore, (D) does not weaken the passage and is incorrect.

(E) states that "the connections between hormone concentrations and reproductive abnormalities is not thoroughly understood." The presence of an imperfect understanding does not form enough of a foundation to cast doubt on the entire study. Moreover, this imperfect understanding could be used to support the passage's conclusion that dioxin is not the cause since we cannot be sure that its effect on hormone concentrations affects reproductive abnormalities. Therefore, (E) does not weaken the passage and is incorrect.

Does that make sense? Please let us know if you have any other questions and best of luck with your studies!

odsimkins on March 1, 2020

This is great. Very helpful. Thank you!