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705-805 (Hard)|   Evaluate Argument|         
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jkkamau
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 03:56
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A. This is inconclusive because the wear and tear could be from grinding or soil friction
B. This choice shows mere correlation and no causation
C. This is not decisive enough. It introduces another location that none of the hypothesis predicts
D. This is irrelevant because it only tells us the seeds are valuable
E. This is the evidence that we need in this case because it shows that pebbles are transported even when reinforcement is not needed
Ans E
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Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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A CORRECT. It tests a unique prediction of the grinding hypothesis. Use as a tool should produce wear.

B It provides indirect information about other species, not this species' behavior.

C Pebble location as described does not clearly distinguish between the two proposed functions.

D Seed nutritional value does not indicate how the pebbles are used.

E It challenges the structural hypothesis but does not directly support the grinding hypothesis or rule out other functions.

The correct answer is A
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 04:29
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Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

Option (E) provides a perfect control group by varying the environmental factor driving the need for tunnel reinforcement:

​If the answer is YES (colonies in stable soil still bring in pebbles): It eliminates the tunnel reinforcement because structural reinforcement isn't necessary in stable soil. This shifts the weight toward the seed-grinding hypothesis.

​If the answer is NO (colonies in stable soil do not bring in pebbles): It suggests that the behavior is directly tied to soil instability, supporting the tunnel reinforcement function and weakening the other.

​Hence, this is the most useful thing to know. Ans. (E)
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 04:34
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So our premises are:
1. Harvester ants transport small pebbles from the soil surface into the nest interior.
2. Harvester ants primarily eat small seeds but they can't eat hard seeds since they can't crack the shell of it.

We have two hypotheses:
Harvester ants transport these small pebbles:
1.To use it as grinding stones to crack the shell of the seeds
2.To reinforce the walls of the nest's tunnels

Lets go through the answer choices:
a.)If interior pebbles has greater surface wear than surface pebble then we may think that ants use it to grind the seed but it does not explain the second hypothesis (Not sufficient)
b.)This answer choice compares other ant species and whether or not they inhabit regions with hard-shelled seeds giving the answer yes or no to this question does not help us to explain the situation we are in. (Let's say "Yes they do inhabit in regions with hard-shelled seeds" so they may use the pebbles to grind the seeds or they have stronger mandibles which can crack the seeds, so this comparison does not give us a proper answer)
c.)We don't know what brood-rearing chambers and etc. So it requires outside information which we don't need to answer the question. (Outside information)
d.)Let's say hard shelled seeds contain more nutrition than soft shelled seeds. Do they need the pebbles to crack the hard shelled seeds just to get more nutrition or do they just gather more soft shelled seeds which they can easily consume. In short, it does not prove that ants use the pebbles to crack open seeds.
e.)If same species of ants still transport pebbles inside the nest, even though the risk of tunnel collapse is not a concern, then we may say that they use the pebbles to grind the seeds.

Answer: E
IMO
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 04:45
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The argument centres on finding information that will bring more clarity to on the purpose of the pebble collection by the harvester ants

a. the wear of the pebbles surface cannot confidently provide clarity to the use of the pebbles. once the pebbles are being moved for either reason, there could be greater surface wear compared to surrounding habitat pebbles.
b. the point doesn't bring clarity to the two options. these other harvester ants can still be bringing in pebbles for both or for just one reason.
c. The argument does not focus on the final deposit location of the pebbles but rather the use of the pebbles.
d. The arguement does not speak on the nutritional content of hard shelled seeds vs soft shelled seeds
e. this option rules out one possible hypothesis on why these ants collect the pebbles, leaving the other hypothesis as more likely to be correct. Correct answer E
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 04:49
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Premise:
Pebbles taken into nest may be used as grinding tool or to reinforce walls which are prone to collapse due to loose soil

What is useful to decide between 2 hypotheses?

(A) More Surface Wear?
This could mean both actually - cannot help us to distinguish

(B) It is talking about ants which already collect pebbles for reinforcement - does not help

(C) it is talking which section of tunnel are these pebbles present. We don’t know exactly what granaries or load bearing section of tunnel is used for in case of ants.

(D) knowing more nutrients is not helpful to decide between hypothesis

(E) this is helpful as it will help to distinguish as if ants transport in this scenario, it will point towards grinding tool function and if they don’t transport it shows they needed pebbles to reinforce. Hence (E) is the answer
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A. most relevant - if no greater surface wear, we can reject the hypothesis
B. make up a large proportion of the local food supply doesn't affect the decision process
C. not relevant
D. more nutrients or not is not relevant
E. doesnt help to decide
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 05:09
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Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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A. Surface wear can't help tell us much. The pebble can be used for support and hence we can't rely on this. Eliminate A.

B. We are only concerned about this species. Eliminate.

C. Can help determine somewhat. But we don't know if the support is needed in rearing chambers. Hence, eliminate.

D. We are not concerned about the nutrition value of the nuts. Can elimiante.

E. This can be used to evaluate. Because if the species that nest in stable soils also transport the pebbles inside, it can be for something else. If not, whatever author has said in the passage can hold true. Hence, E is the best choice.


Option E
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 05:11
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(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface surface wear can result from both uses

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply if No, then it is clear that support is the reason. But, if Yes then the confusion prevails

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels deposi in granaries & load bearning sectiond is to be deposited

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process Irrelevant as already said hard shell seed are important

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interiorCorrect. If they are still collecting then it is forseed cracking..if no, they for tunnel stability

Ans E
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Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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A. Pebble wear could suggest grinding, but worn pebbles could have other causes, so A doesn't help.

B. Information about other ant species does not tell us why this species uses pebbles.

C. The location of pebbles inside the nest it is not as strong.

D. The nutrition of hard seeds does not explain the pebble use.

E. Correct. If ants still carry pebbles into nests where tunnels do not need reinforcement, then the tunnel-support idea becomes irrelevant. This would support the idea that pebbles are used for grinding seeds.

Option E
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Option E
Whether colonies of this species that nest in compact , stable soil....
Btw the 2 hypotheses this one can directly validate or invalidate one of the theses , as here we are validating the use of pebbles to reinforce the walls as the soil is less stable , but in a more stable soil if the ants are still using pebbles then we can come to the conclusion that it is to crack the shells

Option A) - Greater surface wear area - this will not prove any of the hypothesis , because they in normal transportation also we can have some wear and tear so it does not give a direct ans

Option B) - Other harvester ant species - this is not related to both the hypothesis as it is stating about other species and their patters, this can change from area to area so it is not sufficient

Option C) - Brood vs granaries , this also does not give clarity as they are talking a about child bearing vs food areas where there is not direct requirement for structural stability like the tunnels

Option D) - hard shell vs soft , this also does not give a direct ans , even if they are more nutritious then we cannot conclude that the pebbles are for griding alone
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the
local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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A is clear winner

Two hypothesis -
1) pebbles are used as grinding tools
2) pebbles are used as reinforment material.

Need to choose one option which supports either of the hypothesis best.

A) Supports Hypothesis point -1 clearly, but hold on check others.
B) Not a clear statement, it hints for both
C) Location doesn't matter, it dosn't give strong hold for 2nd hypothesis. rather it is more application based.
D) irrelavant, Not looking for nutritious data of shells
E) Weakens the both hypothesis. Not required.
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Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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Premise: Biologists observed ants carrying pebbles and hypothesised two reasons for it
  1. They need to crack hard seeds, which they cannot do without the pebbles
  2. They need it to support their walls made in loose sand
Task: Find an info piece to narrow down to 1 reason

Option A: Not applicable. As both cracking seeds and supporting walls could cause wear
Option B: Other harvester ants are not relevant to our discussion
Option C: While a good one. The position of where it is kept can be contradicted, as pebbles under storage and pebbles being used. Hence, wrong
Option D: Amount of nutrients is irrelevant to our discussion
Option E: Spot on! If ants in stable soil do gather pebbles, then the purpose is grinding. If not, then it validates that it was to support walls


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The pebble has two functions one is for reinforcement of the nest and the other is for the grinding process . So the ans choice should be closest to helping us evaluate these two hypothesis.

A - We do not know how exactly the wear and tear happening for all good reasons it may be happening also due to the grinding . This does not help us exactly .
B - What other harvester ants are doing is irrelevant in analyzing this case
C-.Irrelevant in our evaluation
D- Nutritional difference is not going to help us evaluate the functions of pebbel.
E - Correct this passes variance test if risk of collapse is not an issue then one function is not needed but if there is a risk then the function is necessary.
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:34
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Option A: Worn pebbles would support grinding, but reinforced tunnel pebbles could also experience wear. Helpful but not optimal.
Option B: What other ant species do - Not relevant.
Option C: Where pebbles are deposited - If they are mostly in brood chambers, neither hypothesis is clearly supported.
Can be helpful in granaries or tunnels (but this isn't properly framed) - Not optimal.
Option D: Doesn't tell us why the ants transport pebbles - Not relevant.
Option E: Gives that info -
If yes, structural reinforcement is unlikely -> supports the grinding hypothesis.
If not, it supports the structural reinforcement hypothesis.
So, Answer E is correct
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:39
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E) is correct. If ants carry pebbles even when is no need to reinforce the nest, this supports the seed-crushing hypothesis.

A) Greater surface wear can come from both crushing seeds and building.

B) The behaviour of other species does not help distinguish between the two hypotheses for this species.

C) We do not know where the pebbles are deposited.

D) The passage does not deal with that.
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:48
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First, lets predict the likely answer:

stones likely used for cracking open seeds will be found near them in the habitat and stones used to strengthen the nest walls, will probably be left in vulnerable to collapse places, such as narrow corridors or unsteady supporting walls.

(A) isn't relevant, because it would suggest they were processed by the ants or not and not their use.
(B) isn't immediately relevant, because it's a different species.
(C) Close to our prediction. If Most pebbles are found in problematic areas, with weak walls in the nest, it'd strongly suggest they serve that purpose and if not, then not.
(D) How is this relevant to the pebbles function. This will help find out more about the seeds and not the small stones.
(E) Same species, but a different colony, so less relevant than checking out current colony behavior.

So, (C)
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:51
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IMO : C
in order to evelute which hypothesis is correct
lets go with elimination technique to get to the right answer
A : showing greater surface wear - irrelevant
B: Out of scope
C: keep
D:nutrients ? -- again out of scope
E : stable oil ?? -- irrelevant
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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:55
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pebble's used for seed cracking vs structuring

if either one of them is not required given the circumstances then we can conclude the above.

A -> X (So even if we get pebbles with surface wear the reason for surface wear can be different may be it happened while dragging the pebbles to their habitat)

B -> X (So if we could somehow detect the same for other species we could detect for this species also without comparing them with each other. Not a solid reason)

C -> X (We don't exactly know the purpose of the placements of pebbles in their habitat they can be at the same places for both purposes to support and to crack seeds)

D -> X (I don't think ants will focus more on nutrients would, rather prefer to get food whatever is available)

E -> If the tunnel collapse is not a scenario then working hard enough to bring pebbles to habitat could be for cracking the seeds only. Seems a useful discovery.

Ans - E
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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GMAT Club World Cup 2026 (Day 3): Biologists studying a species of 09 Jul 2026, 06:57
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Premise
Ants carry pebbles into their nests. Two possible functions : grind hard seeds, reinforce next tunnels
Question: which info best helps decide between two hypothesis
Logical gap: need evidence that distinguishes which of the two functions is more likely

Analysing answer choices
A)
if answer is Yes, they are likely used for grinding
if answer is No, grinding is less likely, supporting the reinforcement hypothesis
This is the answer
B) This talks about other species. Incorrect
C) Doesnt distincguish between the two. If not in brood chambers, they could still be in either granaries or tunnels
D)Doesnt explain why pebbles are carried
E) Onesided. Just helps reinforcement hypothesis, not other one

Hence A is the answer.
Bunuel
Biologists studying a species of harvester ant observed that workers regularly transport small pebbles from the soil surface into the nest interior. These ants subsist primarily on seeds, but their mandibles are too weak to crack the shells of the hardest seed varieties available in their habitat. Thus, the pebbles may function as a grinding tool, helping workers process seeds that their mandibles cannot crack. Alternatively, the pebbles may serve to reinforce the walls of the nest's tunnels, which are prone to collapse in the loose sandy soil the colony inhabits.

In order to help decide between the two hypotheses for the pebbles' function, which of the following would it be most useful to know?

(A) Whether pebbles recovered from the nest interior show greater surface wear than pebbles of similar composition collected from the surrounding habitat surface

(B) Whether other harvester ant species that are known to collect pebbles for structural reinforcement also inhabit regions where hard-shelled seeds make up a large proportion of the local food supply

(C) Whether the majority of the pebbles are deposited in the brood-rearing chambers rather than in the granaries or along the load-bearing sections of the tunnels

(D) Whether the hard-shelled seeds that this species cannot crack contain significantly more nutrients than the soft-shelled seeds their mandibles can process

(E) Whether colonies of this species that nest in compact, stable soil - where the risk of tunnel collapse is not a concern - also transport pebbles into the nest interior

 


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