Critical Reasoning

Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One possible cause is dioxin, which paper mills release daily and which can alter the concentration of hormones in fish. 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.

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

(A) Some of the studies that show that fish recover quickly during shutdowns were funded by paper manufacturers.
(B) The rate at which dioxin decomposes varies depending on the conditions to which it is exposed.
(C) Normal river currents carry the dioxin present in the river far downstream in a few hours.
(D) Some of the fish did not recover rapidly from the physiological changes that were induced by the changes in hormone concentrations.
(E) The connection between hormone concentrations and reproductive abnormalities is not thoroughly understood.

Please explain your answer. This one completely blew me off.

Thanks

IMO C.

voodoo_child wrote:Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One possible cause is dioxin, which paper mills release daily and which can alter the concentration of hormones in fish. 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.

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

(A) Some of the studies that show that fish recover quickly during shutdowns were funded by paper manufacturers.
(B) The rate at which dioxin decomposes varies depending on the conditions to which it is exposed.
(C) Normal river currents carry the dioxin present in the river far downstream in a few hours.
(D) Some of the fish did not recover rapidly from the physiological changes that were induced by the changes in hormone concentrations.
(E) The connection between hormone concentrations and reproductive abnormalities is not thoroughly understood.

Please explain your answer. This one completely blew me off.

Thanks

IMO D

Whts OA?

imo B

if the rate at which dioxins decompose in the environment cannot be ascertained then it is wrong to claim that dioxins decompose slowly.

voodoo_child wrote:Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One possible cause is dioxin, which paper mills release daily and which can alter the concentration of hormones in fish. 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.

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

(A) Some of the studies that show that fish recover quickly during shutdowns were funded by paper manufacturers.
(B) The rate at which dioxin decomposes varies depending on the conditions to which it is exposed.
(C) Normal river currents carry the dioxin present in the river far downstream in a few hours.
(D) Some of the fish did not recover rapidly from the physiological changes that were induced by the changes in hormone concentrations.
(E) The connection between hormone concentrations and reproductive abnormalities is not thoroughly understood.

Please explain your answer. This one completely blew me off.

Thanks

Premise: Dioxin decomposes slowly.
Conclusion: Dioxin DOES NOT affect hormone levels in the fish.

To weaken the conclusion, we need to show that -- DESPITE the slow decomposition rate -- dioxin DOES affect hormone levels in the fish. Thus, the correct answer will STRENGTHEN the causal relationship between dioxin and hormone abnormalities in the fish.

One way to support a causal relationship -- to show that X causes Y -- is to show that NO X means NO Y.

Answer choice C: Normal river currents carry the dioxin present in the river far downstream in a few hours. This answer choice connects the ABSENCE OF DIOXIN -- when the mill shuts down, the dioxin is carried downstream -- with the fish's ability to recover: NO X (no dioxin) means NO Y (no hormone abnormalities).

The correct answer is C.

First of all spot the conclusion and the premise

Conclusion: Dioxin is not the cause for reproductive abnormalities in fish

Stated Central Premise: 1) Even if hormones change, the fish are able to restore them quickly due to mill shutdowns

2)Dioxin decomposes slowly

Logic in the argument: X (Dioxin) leads to Y(Change in hormones) leads to Z (reproductive abnormalities)

Can you spot the flaw in author's logic here?
The premise of the author is assuming that X has led to Y. (dioxin has led to change in hormones which is then getting restored due to mill shutdowns). But then he says that although change in hormones has happened, there is no reproductive abnormality. Meaning no correlation between Y and Z.

Now try to find an answer choice that fixes the author's logical flaw.
We can do this if we can find an answer choice wherein X does not lead to Z i.e. Dioxin does not lead to reproductive abnormalities in fish

Careful: The trick words in this qs are immediately downstream and far downstream

Answer C tells us there is no dioxin downstream. So fish cannot be affected by dioxin. Hence the noted reproductive abnormality of fish downstream is not caused by dioxin but by some other factor. Hence Answer C says that THERE IS NO CORRELATION BETWEEN DIOXIN AND REPRODUCTIVE ABNORMALITIES IN FISH. Hence it weakens the logic of the argument. Hence correct answer.


Alternatively eliminate:

Elimination Reasons:

A: Is supporting the central premise (not weakening)

B: Irrelevant/ Out of scope (We are concerned only with dioxin, reproductive abnormality and fishes upstream)

D: We dont know if there is any relationship between physiological changes and fishes reproductive system

E: Looks like a probable answer choice. However the option does not mention explicitly that there is no connection between hormone concentration and reproductive system. Had it mentioned explicitly that there was no connection, then this was the best answer choice.

Hope this helps clear some doubts!!! Best way to get a quick answer to this question is by elimination rather than looking for the right answer choice.

Cheers!!
Turbo Jet