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505-555 (Easy)|   Resolve Paradox|         
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A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 08:30
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Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.
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GMAT Club Official Explanation:



Answer: A.

The conclusion of the passage-that genetically modified (GM) salmon genes disappeared from the wild population-stands in contrast to the earlier finding that those genes had entered wild salmon. To explain this discrepancy, we need a reason why the modified genes, once present, would no longer be detectable in the follow-up study.

(A) provides a compelling explanation: offspring resulting from interbreeding between GM and wild salmon had significantly lower survival rates than offspring of two wild salmon. If these hybrid offspring were less likely to survive and reproduce in the river environment, their genetic contribution would diminish over time. This natural selection effect would explain how the modified genes, although initially present, disappeared from the wild population by the time of the second study. This choice actually resolves the apparent contradiction in the passage.

(B) This strengthens the discrepancy. If GM salmon were more likely to survive due to predator avoidance, one would expect the genes to persist, not disappear.

(C) Does not explain the disappearance of the genes from the wild salmon in the river. The original study already confirmed the presence of those genes in the wild population, so movement of the GM salmon themselves to the ocean is irrelevant and this choice does not address why there are no offspring in the river system.

(D) Trap answer choice, as it only focuses on the Wild Salmon. This does not resolve the disappearance of modified genes from the population in the river environment.

(E) This answer choice is not helpful to explain the discrepancy. Even if a small number of GM salmon had escaped, they were detected in sampling originally, and we would expect that the sampling would increase or at least show some signs of impact. Not seeing any GM genes is not explained by this answer choice.
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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 08:21
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Here, A seems to be the best fit.

In A-> if the offspring of genetically modified and wild salmon had significantly lower survival rates,that means all of them died when the followup test was taken after 3 years, which explains the discrepancy
B-> This does not provide the answer to why there was no trace of GM genes.
C->not a strong reasoning to explain the discrepancy
D->This might explain variation in sampling, but not why the GM genes disappeared.
E->Does not make sense

The answer is A.

Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 08:47
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Information given:
- GM salmon escaped and bred with wild salmon
- In the first season, juvenile wild salmon showed GM genes
- The facility was shut down, remaining GM salmon removed
- Three years later, a large sample of wild salmon showed no GM genes

Question:
- Which option, if true, most helps explain the discrepancy between initial evidence of GM genes and their later absence?

- A: Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
- Explains discrepancy well. The hybrid juveniles existed at first, but because they didn't survive well, their GM genes didn't persist in the population. Therefore, years later, they're gone. Directly resolves the gap.
- Valid

- B: Natural predators tend to avoid genetically modified salmon because of differences in their taste.
- If predators avoided GM salmon, you'd expect GM genes to persist more, not less.
- Invalid

- C: Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
- Does not explain how GM genes vanished from river wild salmon, breeding happened in river, so this is irrelevant for explaining gene drop-off
- Valid

- D: Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
- Might suggest some GM genes are 'elsewhere', but the follow-up tested hundreds, so if they still existed, they'd likely show up. Doesn't directly explain the disappearance.
- Valid

- E: Fewer than ten adult GM salmon escaped before the facility was closed.
- The first study already confirmed GM genes spread, how few escaped doesn't explain why the genes vanished later

Answer: A, Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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The problem presents a paradox: an initial study confirmed the presence of genetically modified (GM) genes in a juvenile salmon population after an escape and interbreeding event, but a follow-up study three years later found no trace of these genes. The task is to find an explanation for this discrepancy. The core of the paradox is understanding why the GM genes, once successfully introduced into the gene pool, disappeared from the population.

The most direct explanation would be a mechanism that actively removed the GM genes or their carriers from the population over the three-year period.

Option (A) provides such a mechanism. If the hybrid offspring of GM and wild salmon had significantly lower survival rates than the offspring of two wild salmon, this would lead to natural selection against the GM genes. The juvenile hybrids identified in the first study would be less likely to survive to adulthood and reproduce. Over a few years, this survival disadvantage would effectively purge the less-fit hybrids, and consequently their GM genes, from the river's gene pool. This resolves the paradox by explaining that while the genes were initially present, they did not persist because their carriers were not evolutionarily fit for the environment.

The other options are less effective. (B) deepens the paradox by giving the hybrids a survival advantage. (C), (D), and (E) provide context but do not offer a direct causal reason for the complete disappearance of the genes from the population after they had already been successfully introduced.

The correct answer is (A).
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Fact 1: After GM salmon escaped and interbred with wild salmon, genetic testing confirmed the presence of GM genes in juvenile wild salmon.
Fact 2: Three years later, a follow-up study found no trace of GM genes in hundreds of wild salmon that were sampled.
Paradox: How could GM genes be present in the salmon population initially but completely disappear three years later?
Let's analyze each answer choice:
A) Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
This choice resolves the paradox. If the hybrid salmon (containing GM genes) had significantly lower survival rates, they would be less likely to survive to adulthood. This explains why GM genes were initially detected in juvenile salmon right after the escape, but three years later, those hybrid offspring had died off, leaving no trace of GM genes in the wild population. The hybrid salmon simply didn't survive long enough to pass on their genes to future generations.
B) Natural predators tend to avoid genetically modified salmon because of differences in their taste.
This doesn't explain why GM genes disappeared. If predators avoided GM salmon, we might expect more GM salmon to survive, not fewer.
C) Genetically modified salmon are more likely to escape into ocean environments than remain in fivers.
This doesn't resolve the paradox. Even if GM salmon tend to leave rivers, the follow-up study was looking for GM genes in wild salmon, which would include any offspring from interbreeding. The location preference of pure GM salmon doesn't explain why the hybrid genes disappeared.
D) Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
This doesn't resolve the paradox. If anything, this might suggest that some salmon with GM genes could have been away during the follow-up study, which would mean GM genes might still be present in the population, not that they disappeared.
E) Fewer than ten adult GM salmon escaped before the facility was closed.
This doesn't explain the discrepancy. The passage already established that GM genes were detected in juvenile wild salmon after the escape, so the number of escaped salmon is irrelevant to explaining why those genes later disappeared.
The correct answer is A.
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premise states

that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system
In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed

Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

inference based CR


A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon. correct option as this can be reason for fall of GM gene offsprings


B. Natural predators tend to avoid genetically modified salmon because of differences in their taste. not a valid reason for no trace of GM gene salmon this option strengthens conclusion

C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers. irrelevant to argument

D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years. does not stand true to argument

E. Fewer than ten adult GM salmon escaped before the facility was closed. does not stand valid to argument

OPTION A is correct

Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
CORRECT : The offspring of genetically modified and wild salmon could have been found in the first spawning season but due to their lower survival rates they could not be found at all after 3 years when the follow - up study was conducted.

B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
INCORRECT - Does not explain the discrepancy.

C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
INCORRECT - Does not explain the discrepancy.

D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
INCORRECT - Does not explain the discrepancy.

E. Fewer than ten adult GM salmon escaped before the facility was closed.
INCORRECT - Does not explain the discrepancy.

Therefore, answer is A.
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The paragraph states that there were no traces of the offspring of GM salmon and the wild Salomon in the second study after three years. The trace was found for the first time after GM Salmon migrated to the river . The reason they were not found because the offsprings could not survive in the river water as they have genes from salmon living in aquaculture facility.

The theory of natural predators , number of GM salmons migrating, the migration to ocean doesn’t support any conclusive evidence of their non-existence three years later.
Hence, the answer is A as, it is believed they could not survive in river as the GM salmon was removed upon shut down of the system. The offsprings could not survive.
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Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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Option A clearly explains this ie genetically modified did not survive hence no traces after 3 years
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Choice A is correct because it tells us that the mixed babies just couldn’t survive in the river so even though you saw their genes right after the escape, those fish died off over the next few years and left no trace. The other options don’t explain the disappearance of the GM genes. B fails because if predators avoid GM salmon, those fish would actually live longer and you’d still find their genes later. C isn’t right since it talks about adult GM fish moving to the ocean, but the follow‐up checked juveniles born in the river, so it doesn’t explain why their offspring vanished. D doesn’t help because wild salmon migration patterns don’t affect gene tests on young fish sampled every year. And E, the small number of escaped adults, might limit initial mixing but can’t by itself account for why every last GM gene was gone after three years that disappearance is best explained by low survival of the hybrids.

Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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My answer is option A

A: If the hybrid offspring are much less likely to survive than pure wild offspring, then over time, their numbers would drop significantly. Three years is enough time for multiple generations or at least for the first generation of hybrids are dead before reproducing, or for next generations to also not survive.This is a strong support for why the gene is not found after 3 years.
B: If it is true then modified gene should be found
C:This could explain fewer number if modified gene will likely be found not the 0 trace
D: Out of scope doesn't explain anything
E: This option doesn't explain why those already present genes aren't found three years later. If it is true then modified gene is likely to be found


Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
Seems Good. Note the words "Significantly lower" and "river environments, hence it's highly probable than juvenile GM died in the 3 years"

B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
This actually opposes the results of 2nd study

C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
One can about to think that what if the GM salmon escaped to ocean and never came back and the salmons in 2nd study were all wild salmon. But note that we don't know that at what age they escape and why they don't come back or if 3 years is sufficient time for them to move to ocean before the 2nd study was conducted

D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
The 2nd study was done post 3 years, which seems like a sufficient time for some of GM salmon to come back, also for the study to be carried out there should have been salmon in river and therefore even if they move to distant spawning ground it does not make much of difference as the time of study a portion must have come back.

E. Fewer than ten adult GM salmon escaped before the facility was closed.
Irrelevant to the discussion. ten, twenty, hundred or just two what difference does it make
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Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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A. Keep, this option explains why GM genes are not found after 3 years in wild salmons as GM salmons offsprings might not have survived.
B. Deepens more the mystery/dispcripensy as there should have been at least some salmons caught after 3 years with GM genes.
C. Incorrect, the follow up study doesn't not mention any description about analysing only river salmons.
D. Incorrect same as option c since there is no limitation of time in the follow up study.
E. Incorrect as we are not concerned about how many left the facility.

Hence Correct answer is Option A.
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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:32
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Let's check each option:

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
If the hybrid offspring (which carry GM genes) have a much harder time surviving in the wild river, they would naturally die off or fail to reproduce as effectively as pure wild salmon. Over three years, with lower survival and potentially lower reproductive success, the GM genes would quickly disappear from the population. This directly explains the disappearance of the GM genes.

B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
This would suggest that GM salmon (and potentially their hybrid offspring) would survive better, not worse. If predators avoid them, they would be more likely to persist and pass on their genes, which goes against the observed disappearance.

C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
This might explain why fewer GM salmon were in the river to begin with, but it doesn't explain why the GM genes, once confirmed to be present in the river's wild population, disappeared. If hybrids were born in the river, their movement to the ocean doesn't automatically mean their genes vanish from the river population unless they also fail to return and breed in the river.

D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
This describes the behavior of wild salmon. It might mean that the sampling in the second study caught a different group of wild salmon. However, it doesn't explain why the hybrid offspring (which were confirmed present) would disappear. If the hybrids also migrate, they might still return. It introduces a variable but doesn't directly address the fitness or survival of the GM gene carriers themselves within the river system over time.

E. Fewer than ten adult GM salmon escaped before the facility was closed.
While a small initial number might limit the initial spread, the first study already confirmed the presence of GM genes in juveniles. The question isn't about how widespread the initial contamination was, but why it disappeared. Even a small initial presence should persist if there isn't a strong negative selection pressure against it.

Therefore, Option A provides the most direct and compelling explanation for the observed discrepancy. If the hybrid offspring (carrying the GM genes) have a significantly lower survival rate in the wild, then over a few generations, those genes would be naturally selected against and effectively purged from the wild population.
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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:33
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We need an option that explains why GM genes did not persist in the population over time.
(A) Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
This directly explains why GM genes disappeared:
The hybrids didn't survive well.

This explains the disappearance of GM genes. Correct.

Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:35
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Answer is A... I’ll explain why, just keep the following things in mind...

- Local River System
- Genetically modified escaped into Local river system
- After few years, the traces were not found...





Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
(This Most helps)


B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
(This is opposite, if predators avoided it, then salmon with GM GENES should have been there)

C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
(Okay, interesting but remember the local river system we decided to keep in mind... This means that it was not local river system since it was escaping into ocean.. Against the stimuli... ELIMINATE)


D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
(Whats few years? Few can be 2 also 3 also or 10 also... not the best choice)


E. Fewer than ten adult GM salmon escaped before the facility was closed.
(Okay so what? How many escaped we are not bothered, there were traces found but later not found)


So A is the best choice....

 


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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:37
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The first study found GM genes in young salmon, but three years later, the second study found none. We need to explain how the GM genes disappeared.

Choice A says the GM-wild hybrids had much lower survival rates. That means those fish likely died off before reproducing, so the GM genes naturally vanished over time. This explains the result perfectly.

Choice B suggests predators avoid GM salmon, which would actually help GM genes survive—not explain their disappearance.

Choice C talks about GM salmon escaping to the ocean, but we’re focused on genes in the river's wild salmon.

Choice D mentions migration patterns, which doesn’t explain why GM genes vanished.

Choice E says few GM salmon escaped, but since the first study still found GM genes, this doesn’t explain why they later disappeared.

So A is the answer.
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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:40
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GM Salmon escaped ——— Interbred ———- GM gene found in Juvenile ———- Facility Shut Down and remaining GM Salmon removed ——— +3 years, No trace of GM genes found

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon........This directly explained why GM genes disappeared.......Correct
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste........ Opposite of what we need......No
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers..... it talks about GM Salmon and not its interbred offspring carrying GM genes........No
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.....But still some traces could be present ......No
E. Fewer than ten adult GM salmon escaped before the facility was closed.......No

A
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GMAT Club Olympics 2025 (Day 6): A research team discovered that 07 Jul 2025, 09:48
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A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Why would there be no traces of GM genes after 3 years, even though GM genes first found shortly after the GM salmon escaped?
May be the genes change somehow
May be the genes are not traceable after a while for some reason
May be all the salmons with GM genes died due to the cross breed
May be they were attacked

A is in line with the pre-thinking. They had pretty low survival rate

B. Natural predators tend to avoid genetically modified salmon because of differences in their taste. This goes in opposite direction
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers. The argument didn't mention the 3 year later investigation was done only in the river. Also, this just mention s the likelihood of the salmon escaping
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years. Irrelevant, we are looking for GM salmons
E. Fewer than ten adult GM salmon escaped before the facility was closed. Irrelvant, we don't care how many escaped the facility
Bunuel
A research team discovered that a species of genetically modified (GM) salmon had escaped from a nearby aquaculture facility and interbred with wild salmon in a local river system. In the first spawning season after the escape, genetic testing of juvenile wild salmon confirmed the presence of GM genes. The facility was then shut down and all remaining GM salmon were removed. Three years later, a follow-up study that sampled hundreds of wild salmon found no trace of GM genes.

Which of the following, if true, most helps to explain the discrepancy between the two studies?

A. Offspring of genetically modified and wild salmon had significantly lower survival rates in the river environment than offspring of two wild salmon.
B. Natural predators tend to avoid genetically modified salmon because of differences in their taste.
C. Genetically modified salmon are more likely to escape into ocean environments than remain in rivers.
D. Wild salmon in the river system typically migrate to distant spawning grounds and return only every few years.
E. Fewer than ten adult GM salmon escaped before the facility was closed.

 


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