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Difficulty:
85%
(hard)
Question Stats:
54% (01:56) correct
46%
(02:19)
wrong
based on 1249
sessions
History
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When fish or mammals ingest the chemical rotenone, enzymes in the digestive tract metabolize most of it, rendering it harmless, but if enough rotenone enters the bloodstream, it can kill them. Wildlife managers who use rotenone in rivers or lakes to reduce fish populations claim that the practice is harmless to aquatic mammals, but clearly if enough rotenone is used to kill fish, mammals must be at risk too.
Which of the following, if true, most seriously weakens the argument?
A. Rotenone can enter a fish's bloodstream directly through the gills.
B. If populations of some fish species are allowed to grow unchecked, they can have disruptive ecological effects that ultimately harm wild mammal populations.
C. When rotenone is introduced into a fast-flowing river, it can travel a considerable distance downstream before breaking down.
D. For most aquatic mammals, fish constitute a substantial portion of their diet.
E. Chemicals that in the past have been used to reduce fish populations have considerably higher toxicity to aquatic mammals than rotenone does.
Which of the following, if true, most seriously weakens the argument?
A. Rotenone can enter a fish's bloodstream directly through the gills.
B. If populations of some fish species are allowed to grow unchecked, they can have disruptive ecological effects that ultimately harm wild mammal populations.
C. When rotenone is introduced into a fast-flowing river, it can travel a considerable distance downstream before breaking down.
D. For most aquatic mammals, fish constitute a substantial portion of their diet.
E. Chemicals that in the past have been used to reduce fish populations have considerably higher toxicity to aquatic mammals than rotenone does.
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Updated on: 01 Feb 2026, 06:45
Originally posted by MartyMurray on 17 Apr 2024, 15:05.
Last edited by MartyMurray on 01 Feb 2026, 06:45, edited 2 times in total.
Last edited by MartyMurray on 01 Feb 2026, 06:45, edited 2 times in total.
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When fish or mammals ingest the chemical rotenone, enzymes in the digestive tract metabolize most of it, rendering it harmless, but if enough rotenone enters the bloodstream, it can kill them. Wildlife managers who use rotenone in rivers or lakes to reduce fish populations claim that the practice is harmless to aquatic mammals, but clearly if enough rotenone is used to kill fish, mammals must be at risk too.
The conclusion of the argument is the following:
if enough rotenone is used to kill fish, mammals must be at risk too
Not much support for the conclusion is provided, but the passage does say the following:
When fish or mammals ingest the chemical rotenone ... if enough rotenone enters the bloodstream, it can kill them.
We see that the reasoning of the argument is basically that, since rotenone can kill fish or mammals if enough enters their bloodstreams, if there's enough rodenone around to kill fish by entering their bloodstreams, there's also enough to do the same to mammals.
Which of the following, if true, most seriously weakens the argument?
This is a Weaken question, and the correct answer will cast doubt on the conclusion.
A. Rotenone can enter a fish's bloodstream directly through the gills.
This choice is interesting. After all, if rotenone can enter a fish's bloodstream directly through the gills, then maybe it's much easier for rotenone to kill fish than it is for it to harm mammals. After all mammals don't have gills. So, since rotenone can get into fish's bloodstreams in this way that's unique to fish, it's possible that rotenone would kill fish while being harmless to mammals.
So, while this choice doesn't prove that mammals won't be at risk if enough rotenone to kill fish is used, it does cast doubt on the conclusion "clearly if enough rotenone is used to kill fish, mammals must be at risk too." After all, if it's even possible that there's a key difference between fish and mammals that allows rotenone to kill fish without harming mammals, then its not clear tha mammals "must" be at risk.
So, this choice seems to be correct.
At the same time, it makes sense to be a little cautious with this choice since. After all, for this choice to be correct, we have to decide without being told that rotenone has no easy way to get into the bloodstreams of mammals.
Yes, we can use common knowledge in evaluating CR answer choices, but does common knowledge include knowing that mammals don't have gills and that mammals don't have anything like gills through which rotenone could enter their bloodstreams? Probably, but this choice is somewhat unique in how far it takes the common knowledge aspect of CR.
So, we can keep this choice while being prepared for the possibility of seeing a better one that even more clearly weakens the argument.
Keep.
B. If populations of some fish species are allowed to grow unchecked, they can have disruptive ecological effects that ultimately harm wild mammal populations.
This information indicates that using rotenone to control fish populations can benefit mammals.
At the same time, the fact that the practice of using rotenone can benefit mammals doesn't mean that rotenone doesn't also harm mammals. So, this choice doesn't cast doubt on the conclusion.
Eliminate.
C. When rotenone is introduced into a fast-flowing river, it can travel a considerable distance downstream before breaking down.
If anything, this choice strengthens, rather than weakens, the case for the conclusion. After all, if rotenone can travel a considerable distance before breaking down, then there may be many opportunities for it to harm aquatic mammals.
Eliminate.
D. For most aquatic mammals, fish constitute a substantial portion of their diet.
If anything, this choice strengthens, rather than weakens, the case for the conclusion.
After all, if fish constitute a substantial portion of the diet of most aquatic mammals, then if rotenone is getting into fish's bloodstreams, it may also get into the bloodstreams of aquatic mammals when they eat fish. So, by eating fish, aquatic mammals may consume enough rotenone to be harmed by it.
Eliminate.
E. Chemicals that in the past have been used to reduce fish populations have considerably higher toxicity to aquatic mammals than rotenone does.
This choice presents an irrelevant comparison. After all, regardless of whether other chemicals are more toxic to mammals than rotenone, it could still be the case that rotenone will harm aquatic mammals. In other words, the fact that something else is worse doesn't mean that rotenone is harmless.
Eliminate.
Since none of the other choices weaken the argument at all, the correct answer must be (A).
The conclusion of the argument is the following:
if enough rotenone is used to kill fish, mammals must be at risk too
Not much support for the conclusion is provided, but the passage does say the following:
When fish or mammals ingest the chemical rotenone ... if enough rotenone enters the bloodstream, it can kill them.
We see that the reasoning of the argument is basically that, since rotenone can kill fish or mammals if enough enters their bloodstreams, if there's enough rodenone around to kill fish by entering their bloodstreams, there's also enough to do the same to mammals.
Which of the following, if true, most seriously weakens the argument?
This is a Weaken question, and the correct answer will cast doubt on the conclusion.
A. Rotenone can enter a fish's bloodstream directly through the gills.
This choice is interesting. After all, if rotenone can enter a fish's bloodstream directly through the gills, then maybe it's much easier for rotenone to kill fish than it is for it to harm mammals. After all mammals don't have gills. So, since rotenone can get into fish's bloodstreams in this way that's unique to fish, it's possible that rotenone would kill fish while being harmless to mammals.
So, while this choice doesn't prove that mammals won't be at risk if enough rotenone to kill fish is used, it does cast doubt on the conclusion "clearly if enough rotenone is used to kill fish, mammals must be at risk too." After all, if it's even possible that there's a key difference between fish and mammals that allows rotenone to kill fish without harming mammals, then its not clear tha mammals "must" be at risk.
So, this choice seems to be correct.
At the same time, it makes sense to be a little cautious with this choice since. After all, for this choice to be correct, we have to decide without being told that rotenone has no easy way to get into the bloodstreams of mammals.
Yes, we can use common knowledge in evaluating CR answer choices, but does common knowledge include knowing that mammals don't have gills and that mammals don't have anything like gills through which rotenone could enter their bloodstreams? Probably, but this choice is somewhat unique in how far it takes the common knowledge aspect of CR.
So, we can keep this choice while being prepared for the possibility of seeing a better one that even more clearly weakens the argument.
Keep.
B. If populations of some fish species are allowed to grow unchecked, they can have disruptive ecological effects that ultimately harm wild mammal populations.
This information indicates that using rotenone to control fish populations can benefit mammals.
At the same time, the fact that the practice of using rotenone can benefit mammals doesn't mean that rotenone doesn't also harm mammals. So, this choice doesn't cast doubt on the conclusion.
Eliminate.
C. When rotenone is introduced into a fast-flowing river, it can travel a considerable distance downstream before breaking down.
If anything, this choice strengthens, rather than weakens, the case for the conclusion. After all, if rotenone can travel a considerable distance before breaking down, then there may be many opportunities for it to harm aquatic mammals.
Eliminate.
D. For most aquatic mammals, fish constitute a substantial portion of their diet.
If anything, this choice strengthens, rather than weakens, the case for the conclusion.
After all, if fish constitute a substantial portion of the diet of most aquatic mammals, then if rotenone is getting into fish's bloodstreams, it may also get into the bloodstreams of aquatic mammals when they eat fish. So, by eating fish, aquatic mammals may consume enough rotenone to be harmed by it.
Eliminate.
E. Chemicals that in the past have been used to reduce fish populations have considerably higher toxicity to aquatic mammals than rotenone does.
This choice presents an irrelevant comparison. After all, regardless of whether other chemicals are more toxic to mammals than rotenone, it could still be the case that rotenone will harm aquatic mammals. In other words, the fact that something else is worse doesn't mean that rotenone is harmless.
Eliminate.
Since none of the other choices weaken the argument at all, the correct answer must be (A).
05 Jun 2024, 23:55
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MartyMurray
Hi MartyMurray
I'm not sure that I agree with above explanation. I think, (A) is not even remotely close. I would request you to review my below logical rejection for (A).
Premise: When fish or mammals ingest the chemical rotenone, enzymes in the digestive tract metabolize most of it, rendering it harmless, but if enough rotenone enters the bloodstream, it CAN kill them
Conclusion: if enough rotenone is used to kill fish, mammals MUST be at risk too.
Two things i noted:
1. Argument goes from CAN to MUST
2. Here, no comparison has been made between the ''risk'' if enough rotenone is used.
Quote:
This seems to be a ''so what?'' answer. I need an option which says that: Hey, mammals may not be at risk
All this option says is ''Rotenone CAN enter fish's bloodstream directly. Does it say that, Rotenone enters directly more easily in Fish than in mammals? I don't think so.
Just because fish will be killed immediately, doesn't mean mammal may not be at risk.
