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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 20:27
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Let's breakdown each sentence
1. Algae naturally covers....protect their eggs. - Background Info
2. To Test....the remaining sections undisturbed. They then monitored egg laying across all sections over the following week. - Explanation of the experiment carried out. Background Info
3. The section from which the algae had been removed had significantly fewer intact fish eggs than the undisturbed section - Reasoning for the argument/Premise
4. leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs - Conclusion

We have to undermine the reasoning mentioned above in 3.

A - This just talks about fish's preference. Does not help in undermining the rationale as to why algae facilitates reproduction - Incorrect.

B - Scraping causes abrasion damage to the underlying substrate that reduces its suitability for egg laying site - This gives us another reason as to why the eggs were inact. It is not the algae but the underlying subtrate which makes the surface suitable for egg laying. - Correct.

C - This is additional information and focuses on the undisturbed part only - Incorrect.

D - We are not concerned with whether the eggs hatch or not. The question is specific about the eggs being intact. - Incorrect.

E - Again, out of scope. Incorrect.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 20:34
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B.

The conclusion: algae itself helps eggs (attachment + protection), inferred from fewer intact eggs on scraped sections. The gap: the scraping is the treatment, so any effect of the act of scraping (not the absense of algae) is a confound.

B nails it, if scraping abrades the substrate and makes it a worse egg site, then fewer eggs could come from the damage, not the missing algae. The two variables are tangled, so the experiment can't isolate algae as the cause. The reasoning is Dead on arrival.

Wrong ones
A - Predicts more eggs on scraped sections. Wrong direction here
C - Algae protects eggs. That supports the conclusion.
D - Quibbles with the success metric, however does not touch the link of scraping to the result. Not in scope.
E - Long term oxygen effects. Wrong timescale and irreelvant.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 21:40
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Conclusion: The algae facilitates fish reproduction by proving attachment sites & protective covering for eggs.
Reasoning: The section from which algae had been removed had significantly fewer intact eggs than the undisturbed sections.

To weaken teh arguement, we need to find another evidence or explantion for why the sections from which algae is removed has lesser intact eggs than undisturbed sections.

A - this is contradicting the observation/fact. we jnow that fact/observation cannot be challenged.
B - this explains the lower numbers of intact eggs at scraped area because they got damaged by abrasion. Eggs were laid there, but it got damaged, undermines the conclusion.
C - It is supporting the conclusion, so it's a strengthner.
D - Out of scope. Reproductive success has nothing to do with the reasoning & conclusion.
E - Effect of Algae growth on oxysen avalibility is not relevent to the arguement.

Answer: B
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 22:40
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Researchers say that: They removed algae from some reef sections. Those sections had fewer intact fish eggs. Therefore, algae helps fish reproduce by providing attachment sites and protection for eggs. To weaken we need to show that something other than the absence of algae has caused the fewer eggs.

(A) Fish prefer laying eggs on bare reef surfaces.

If this were true removing algae should have led to more eggs, not fewer. Eliminate A

(B) Scraping algae damages the reef surface, making it a poor place for fish to lay eggs.

This makes sense. Maybe it wasn't the lack of algae that reduced egg numbers and maybe the scraping itself damaged the reef making it unsuitable for egg laying.
This directly weakens the conclusion. Hold B

(C) Algae protects eggs from predators and strong currents. This directly supports the conclusion that algae helps protect eggs. Hence it strengthens the argument instead of weakening it. Eliminate C

(D) Egg hatching rate is a better measure of reproductive success than the number of surviving eggs.
Conclusion is based on the number of intact eggs. Whether another measure is better doesn't explain why the original observed difference occurred. Eliminate D

(E) Too much algae can eventually reduce oxygen levels. Not relevant since it talks about aglae growth and not normal levels of algae as in the argument. Eliminate E

Answer: B
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 23:10
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Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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conclusion - fish layed more eggs in the section from where algae was not removed as algae provides protection and attachment sites.
A -> directly conflicts with the conclusion. no reasoning.
B -> KEEP gives a possible reason other than the one concluded by researchers.
C -> Strengthen the argument
D -> not as direct as B
E -> irrelevant
thus, OPTION B is correct.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 23:12
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B is correct. The researchers assume that fewer intact eggs in scraped sections resulted from the absence of algae. However, if scraping itself damaged the reef surface and made it less suitable for egg-laying, then the reduced number of eggs could be caused by substrate damage rather than the removal of algae. This provides an alternative explanation and seriously weakens the conclusion that algae facilitates reproduction.

A is incorrect because if fish prefer bare reef surfaces, removing algae should increase egg-laying. C strengthens the argument by giving a mechanism through which algae protects eggs. D questions the measure of reproductive success but does not show that algae was not responsible for the observed difference. E discusses a long-term effect of excessive algae growth and is unrelated to the experiment's conclusion.
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 23:17
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So the researchers scrapped the algae and these sections had fewer intact eggs, researchers link that this means the algae must provide attachement sites and protective covering.

A - Fish prefer bare surfaces over algaw, which seems to cut against the conclusion, but it actually makes the result harder to explain rather than offering an alternative cause for it. Also think if fish prefer bare rock then we'd expect more eggs in scraped sections - eliminate
B - scraping causes abrasion damage to the underlying substrate. this is devastating, as it introduces a new factor that sections weren't just largely algae free they were damaged - keep
C - this option would strengthen the conclusion as it directly supports the claimed mechanism, so eliminate
D - this doesn't weaken the conclusion but provides another view which doesnt mean the researchers view is weaker, the correct answer needs to undercut the causal link between algaw and egg count - eliminate
E - irrelevant to this trial, it describes downsides of exccessive algae growth - eliminate
Answer B
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 23:21
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The answer is B. The argument's logic is that the algae-scraped sections had fewer intact eggs than undisturbed sections therefore algae facilitates fish reproduction. B is the correct answer because it introduces a new factor that could have impacted the number of intact eggs. The lower number of eggs could be from damage from the algae removal rather than the absence of the algae itself which undermines the claim.

A is incorrect because does not explain the result observed in the experiment. Knowing that bare reef surfaces could attract egg laying does lean into the idea that fish would've preferred a surface without algae, but that doesn't refute the conclusion that algae helps facilitate egg laying.

C supports the researches conclusion rather than weakens it. Algae providing physical protection helps facilitate egg laying and is specifically mentioned in the conclusion. Incorrect

D is incorrect because it talks about hatching while the conclusion is based upon egg presence. Though this information might be useful for the long term evaluation of if algae, the conclusion is based upon the experiment studying egg presence.

E is irrelevant to the conclusion and the study. The conclusion that algae facilitates fish reproduction is not addressed. Unchecked algae growth is an unrelated problem.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 13 Jul 2026, 23:50
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the correct answer here is B

Conclusion: the researchers concluded that the algae facilitate fish reproduction by providing attachment sites and protective covering for eggs.

cause-effect relationship; the correct answer will be something that says the scraping is the reason for the area to have lesser fish eggs

Option A - this doesn't weaken the conclusion, it talks about bare reef surface
Option b - this is exactly on point with our pre-thinking. The scraping made it unsuitable as an egg laying site
Option C - this talks about predators and currents; not relevant
Option D - this is completely out of scope. Talks about post hatch reproductive success. Not relevant
Option E - again out of scope. This talks about what happens when left unchecked

only correct answer is option B

thanks,
Swetha

Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 00:23
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I was confused betweeen B & D, But chose B for the following reason-
In the sea/oceans, coral reefs are undisturbed. When the researcher took 20 reefs and scraped off algae and its surface got disrupted than it's natural form, obviously eggs would not stay. It would give false result.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 01:26
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Premise: Undisturbed section - more fish
Conclusion: Algae facilitates fish reproduction

(A) Changing the premise - not weakens
(B) Weakens - answer
(C) Strengthens
(D) Irrelevant
(E) Irrelevant
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 01:35
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IMO ANS is - B
So I Pre thinking another reason when we are removing algae and because of human touch some issue happened and hence fish eggs are less now on touched area.
I got similar option B so I went with this option I feel this question is comparably easier to other CR questions. Answer choice option also I eliminate easy.
A - If A is true then eggs should be more in bare beef before the research also but yes It could be one of the weakener answer choice if we says our fish / data points are not equal I haven't this before when I'm answering the question
b - Correct - I'm assumed fish are normal and then I pre think so - something happened when human removed touched the algae side so this could be the reasons less eggs sticking now.
c- this is strengthener
d - egg hatched is irrelevant here.
e - it gives extra info if algae is overgrown it may cause issue again irrelevant on this research ask weakener

SO in my opinion B is Answer.
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 01:44
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In this CR, we need to weaken the researchers reasoning which says - after removing algae from the site there were fewer intact eggs as compared to those sites which still had algae present.
The researchers in their conclusion did not consider any other factor responsible for lower intact eggs present in site with no algae.

A) This option is irrelevant as it would make the results complicated and this option does not undermine researchers reasoning
B) if the process of removing algae caused damage to the site and reduces the suitability as egg laying site then we have an alternative reason to prove the lower intact eggs in sites with algae absent. - CORRECT
C) this strengthens the protection role played by algae and hence strengthen the researchers conclusion
D) It is a definition of reproductive success only and does not contribute to weakening the researchers reasoning
E) it is a long-term consequence and does not give any detail on the immediate research and thus does not weaken researcher's reasoning.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 02:23
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Aim - to check how Algae affect the egg laying behaviour of fish.
Data observed - section without algae had significantly fewer eggs than the section with algae.
Derived conclusion- Algae facilitate fish reproduction by providing attachmment and protection benefit for eggs.

Logic - Observed data about one specific behaviour is used to conclude a broader conclusion (Typical Gmat).
Pre thinking - At the same time we cannot deny that the algae does'nt facilitate, we should look for an option that provide an alternate cause of less eggs in the region withh no algae.

In simple terms,
Data - Alage ----> more eggs and no Algae ------> less eggs
Therefore, Algae caused More eggs
What if, there is some other reason that caused less eggs, in that case the conclusion will not follow and we'll find our valid weakener.
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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A - even if fishes preferred laying eggs on bare reef surfaces, we cannot deny the fact provided in the argument that the region with algae had significantly more eggs.
B - so scraping the algae caused damage to the surface of the reef that reduced its suitability for an egg-laying site. This gives us an alternate reason why the region without algae had fewer eggs.
C - this is only telling us about the benefits of algae region, which is irrelevant.
D - this is weakening the wrong data in the argument, which is irrelevant to the link which we are trying to weaken.
E - this is giving us more information about the algae growth, which is irrelevant to our argument.


hence, option B is the correct choice.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 02:25
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The researcher conclude that algae helps fish reproduction because the sections w/o algae had fewer intact eggs.

A actually goes against the findings. If fish prefer bare surfaces, we would expect more eggs in the scraped sections, not fewer. Eliminate
B sounds good imo. Removing the algae also damages the reef surface. So the lower no. of eggs could be because the scraping damaged the egg-laying site, not because the algae itself was helping. Keep
C strengthens the conclusion. It directly explains how algae protect the eggs. Eliminate
D is out of scope. The researchers compared intact eggs, not which measure of reproductive success is better. Eliminate
E is irrelevant. Long term effects of excessive algae growth dont explain the results of this experiment. Eliminate

Ans : B
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 03:19
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(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas. This actually contradicts as fish layed eggs preferentially on algae surfaces.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site. Correct. It is not the absence of algae, but the disturbance caused problem in the substrate.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents. Strengthens showing absence of algae is the cause of absence of eggs.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching. Irrelevant as we are concerned with the proportion of eggs laid.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations. Irrelevant as we are concerned with the affect of algae on laying of eggs by fish.

Ans B
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 03:28
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A. This is contrary to the observation made above because if that was the case then we should expect more eggs where algae was removed
B. This clearly undermines the causal conclusion derived hence correct
C. This provides no relevant information to undermine the prevailing conclusion
D. We do not need an alternative but something related to the heart of the argument
E. This does not as our concern is about egg layering not oxygen
Ans B
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 03:32
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Conclusion: Algae facilitates fish reproduction by providing attachment sites and protective covering.

A) This says fishes prefer reef surfaces, if they do then there would be more eggs in the section where algae was removed. But we can see there are egg laying but comparatively low. Eliminate.
B) This says the fewer eggs were coz of the abrasive surface of the removed algae section. This gives alternate reason for the conclusion. Keep it.
C) This more like strengthening the conclusion. Eliminate.
D) This talks about hatching of eggs. Feels out of context. Eliminate.
E) This also talks about oxygen availablity, seems out of scope. Eliminate.

Answer is B.
Bunuel
Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs. To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks. The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas.
(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.

 


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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 04:20
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A-incorrect: if fish naturally prefer bare surfaces, it makes the experimental results even more confusing. It does not provide an alternative.
B-Correct: If damaged surfaces discourage egg-laying, the study cannot specifically say algae is the cause which undermines the reasoning.
C-incorrect: confirms that algae provides physical protection directly which supports the researcher's conclusion and strengthens the argument.
D-incorrect: talks about measuring reproductive success but we need to know whether algae caused the observed difference.
E-Incorrect: This is irrelevant by talking about long-term effects of excessive algae growth.
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GMAT Club World Cup 2026 (Day 6): Algae naturally covers large 14 Jul 2026, 04:46
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Algae naturally covers large sections of coral reefs and is commonly used by several fish species as a surface on which to lay and protect their eggs.

To test whether algae coverage affects where and how successfully fish lay eggs, researchers selected 20 reef sections and scraped all algae from half of them, leaving the remaining sections undisturbed. They then monitored egg-laying across all sections over the following weeks.

The sections from which algae had been removed had significantly fewer intact fish eggs than the undisturbed sections, leading the researchers to conclude that algae facilitates fish reproduction by providing attachment sites and protective covering for eggs.

Which of the following, if true, most seriously undermines the researchers' reasoning?

Pre-thinking: Some other factor other than algae providing attachment sites and protective covering for eggs may be responsible for facilitating fish reproduction.


(A) Fish in the study area preferentially lay their eggs on bare reef surfaces rather than on algae-covered areas. This actually strengthens the researcher's reasoning that algae faciliates fish reproduction and protect fish eggs.
Incorrect

(B) Scraping algae from reef surfaces causes abrasion damage to the underlying substrate that reduces its suitability as an egg-laying site.
This provides an alternative explanation why there were fewer intact fish eggs on the sections from which algae had been removed. The algae don't necessarily faciliate fish reproduction by protecting fish eggs but other factor damages them.
Correct

(C) In the undisturbed sections, algae provides physical protection for fish eggs against predators and strong currents.
This is an additional information stating that algae provides protection to fish eggs not only by providing covering sites and covering eggs but also by protecting against predators and strong currents. This strengthens the researcher's reasoning
Incorrect

(D) The proportion of eggs that successfully hatch is a more accurate indicator of reproductive success than the number of eggs that survive to hatching.
This shifts focus from underlying reasoning to another way of reasoning and provides another way to analyze algae's role in fish reproduction but does not undermine the researcher's reasoning in a substantial way.
Incorrect

(E) If left unchecked, algae growth can eventually overgrow reef sections to the point where it reduces oxygen availability for fish populations.
This is an additional information unrelated with the researcher's conclusion. The conclusion is about algae and fish reproduction and not about their survival.
Incorrect

IMO B
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