One summer, floods covered low-lying garlic ﬁelds situated in a region

Question

One summer, floods covered low-lying garlic ﬁelds situated in a region with a large mosquito population. Since mosquitoes lay their eggs in standing water, ﬂooded ﬁelds would normally attract mosquitoes, yet no mosquitoes were found in the ﬁelds. Diallyl sulﬁde, a major component of garlic, is known to repel several species of insects, including mosquitoes, so it is likely that diallyl sulﬁde from the garlic repelled the mosquitoes.

Which of the following, if true, most strengthens the argument?

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.

(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.

(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer.

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

Mosquito Repellent

Step 1: Identify the Question 
 
The phrasing strengthens the argument indicates that this is a  Strengthen the Argument  question.

Step 2: Deconstruct the Argument

normally: floods attract mosquitoes

BUT: no mosquitoes in flooded garlic fields

Step 3: Pause and State the Goal

The goal is to eliminate any answer choice that does not strengthen the conclusion. The right answer will make it more likely that the diallyl sulfide repelled the mosquitoes. The answer might do this by showing that the  mosquitoes weren’t actually repelled by some other, unknown factor .

Step 4: Work from Wrong to Right

(A) If the argument stated that mosquitoes also avoided flooded onion fields, this answer would strengthen the argument, since it would suggest that the mosquitoes’ behavior was due to something that onions and garlic have in common. However, the argument doesn’t provide any information about onions related to mosquitoes, so a comparison between onions and garlic doesn’t affect the conclusion.

(B) This answer choice provides another reason for the absence of mosquitoes: there were significantly fewer of them in the area. If this other factor was actually to blame, it’s less reasonable to claim that the diallyl sulfide repelled the mosquitoes. So, this answer choice weakens, not strengthens, the conclusion.

(C) According to this answer choice, most of the garlic plants had died by the end of the summer. This does not have a strong effect on the conclusion, since it isn’t clear how long the garlic plants survived, or what happens to the diallyl sulfide in the plants when they die. In addition, this tends to weaken the argument more than it strengthens it. If the garlic plants weren’t even in the field for a portion of the summer, it’s less likely that their presence was what repelled the mosquitoes.

(D) CORRECT . The argument states that mosquitoes, which are repelled by diallyl sulfide, were not found in the fields. The answer choice adds the information that other insects, which are not repelled by the substance, were found in the fields. So, there is a direct relationship between being repelled by diallyl sulfide, and being repelled from the fields described in the argument. This provides evidence that diallyl sulfide was responsible for the effect as opposed to some other factor that might repel all types of insects.

(E) This answer choice attempts to strengthen the claim that mosquitoes are repelled by garlic. However, the argument states as fact that garlic repels mosquitoes. Since this is already known to be true, adding additional evidence for it does not strengthen the argument. The conclusion of the argument is that the daillyl sulfide in the garlic is what repels the mosquitoes; this answer does not clarify what role diallyl sulfide plays.

akhil911 · Accepted Answer

One summer, floods covered low-lying garlic ﬁelds situated in a region with a large mosquito population. Since mosquitoes lay their eggs in standing water, ﬂooded ﬁelds would normally attract mosquitoes, yet no mosquitoes were found in the ﬁelds. Diallyl sulﬁde, a major component of garlic, is known to repel several species of insects, including mosquitoes, so it is likely that diallyl sulﬁde from the garlic repelled the mosquitoes.

Which of the following, if true, most strengthens the argument?

The Gmat loves to test logic similar to thats given here in this argument.
Premise - No mosquites found in garlic fields flooded with water.
Conclusion - DS ( Dialllyl Sulphide) found in garlic repelled the mosquitoes.

This argument is of type X ->Y where X is DS and Y is mosquitoes repelled.
We can strengthen the argument in two ways :
Either we limit out other choices which can result in Y or we can provide additional evidence that X results in Y.

Here Choice D is such an answer choice where we are limiting other factors which can result in mosquito repeals.

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.

(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.

(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer.
 Limiting out other potential factors which could repeal mosquitoes. If other insect species , which are not repelled by DS then it is possible that DS is responsible for mosquito repeals.
Lets take an opposite of this answer choice - If many other insect species were also not found in the fields this particular year - this would mean that some other factor such as maybe extreme environment or poor water quality could result in insect species getting repelled (including mosquitoes).
 
(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

WillGetIt · Answer

Hello,

I think analysis of this question is as follows:

Premise 1: Garlic fields in region with high mosquito population

Premise 2: Since mosquitoes lay their eggs in standing water, ﬂooded ﬁelds would normally attract mosquitoes

Counter premise: Yet no mosquitoes were found in the ﬁelds.

Conclusion: Reason for low population of mosquito's is Diallyl sulﬁde, a major component of garlic, which is known to repel several species of insects, including mosquitoes.

So whats going on here? A field located in area of high mosquito population and additional risk of even higher mosquito population (due to standing water, flood etc) than the surrounding high population mosquito area.

Question stem: Which of following strengthen the argument???

I don't think no cause - no effect is appropriate justification for correct choice.

Argument can be strengthen in one of following ways:

1. Stating a unstated assumption

2. Support or elaborate existing premise

3. New support premise

etc.......

Analysis of answer choices:

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.

Out of Scope

(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.
 
Population of mosquito in a particular year has nothing to do with conclusion. Even if population is higher, same or smaller (at most we are only concerned about relationship of population from surrounding area), it does not have any impact

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.

So that means, it this is the case then probably something else is responsible for low mosquito population. Possibly a weakner at most, but mainly it have no impact on argument.

(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer.

CORRECT. Well this is  new supporting premise .

Many other species not repelled by diallyl sulﬁde are available in the fields. So, we have a reason to believe that since diallyl sulﬁde repeal mosquito not some other insect species hence mosquito population is low.

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

Out of scope again. Similar to A

Regards
Vikas

Please hit kudos, if it helps. It will be very motivating.

WaterFlowsUp · Answer

Ahh this is the first question i lay my hands from the new og. Also thanks for posting such questions.
D. Sulphide present ----> no mosquito
Therefore no cause ---> no effect.
Option d says
No problem from sulphide therefore other insects are present

BrainLab · Answer

To be honest it's a really poorly constructed question for an official one. So we are looking fot something that says that garlic field repelled the mosquitoes...

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.  --> clearly out of scope 
(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.  --> Great, if true it only weakens the argument that garlic fields repelled mosquitoes

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi  -->one more weakener, if garlic plants have beend killed, so if garlic fields have been killed, then it's 100% that somethin other then garlic field repelled insects... 
(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer  --> derived on the answer choices by POE, as this answer choice doesn't convince me, BUT others are just worse.... 
(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds  --> we are interested in the effect of garlic fields on insects... actually one more weakener

septwibowo · Answer

My analysis :

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.
 Irrelevant

(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.
 Where is diallyl sulfide here? We can't find any relationship with diallyl sulfide. Incorrect. 
Moreover, if last year there were no flood, how mosquito could grow when garlic releases the diallyl sulfide?

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.
 Weaken. It says that there is another reason rather than sulfide.

(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer.
 Correct. It strengthens our argument.

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.
 Irrelevant.

SJ1295 · Answer

Why not option E?

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic,  such as marigolds.  ---> (Giving an example of other plats)

It states that the mosquitoes are easily influenced by toxins in plants other than garlic, such as marigold

Please note that DS is not toxin, so not any toxin/pesticide/factor but DS is responsible for repelling the mosquito.

GMATNinja  please help.

GMATNinja · Answer

The author concludes that "diallyl sulfide from garlic repelled the mosquitoes." This conclusion is supported by the following facts:

No mosquitoes were found in the fields, despite the fact that the region has a large mosquito population.  
 Diallyl sulfide is known to repel mosquitoes.

Let's now consider (E):

It's hard to see how this is relevant to the argument. We're trying to strengthen the idea that diallyl sulfide from the garlic repelled the mosquitoes. But (E) only tells us about plants  other  than garlic, so it doesn't have any direct effect on our conclusion.

From another angle: we already know that diallyl sulfide is found in garlic, and that it repels mosquitoes. This answer choice doesn't add anything new to suggest that the diallyl sulfide from the garlic repelled the mosquitoes in this instance.

Since it isn't relevant to the argument, we can eliminate (E).

I hope that helps!

PyjamaScientist · Answer

Hi  AndrewN  &  MartyTargetTestPrep ,

This question got me thinking a lot. As it's a strengthen type question, we need to add weight to the conclusion or provide a new piece of information that affirms the causality of the argument.

But,  frankly , none of the choices seems to do that for me. I zeroed on (D) after POE. All the choices were not even relevant to the argument. But, (D) too, barely strengthens the cause-effect relationship stated in the conclusion.

The author's conclusion is:  "it is likely that diallyl sulﬁde from the garlic repelled the mosquitoes" , we need information that strengthens this idea. But, (D) instead brings in a piece of information that has no bearing on the conclusion. (D) says that,  "Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer."  Fine. But, does that strengthen the point that  "diallyl sulﬁde repelled the mosquitoes" ? I feel there's still a gap and (D) does not bridge any.

The correct answer should have had something that really "increased my belief" into the statement that  "diallyl sulﬁde DID repel the mosquitoes" , does the information provided in (D) do that? I am not sure how.

AndrewN · Answer

Hello,  PyjamaScientist . I think your analysis is missing a crucial piece of information from the passage, the premise that builds up to the argument:  Diallyl sulﬁde, a major component of garlic, is known to repel several species of insects, including mosquitoes . If diallyl sulfide is  known  to repel mosquitoes, and if  many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer , then it seems reasonable to implicate diallyl sulfide in having kept the mosquitoes at bay.

I agree that no other answer choice is even remotely close to strengthening the argument. As much as possible, you want to see if you can put your finger on the straight-arrow logic that governs the flow of ideas within the passage. You may want to see  this question  on leaf beetles that follows a related path.

Thank you for thinking to ask. It is a pleasure to be mentioned alongside Marty.

- Andrew

MartyTargetTestPrep · Answer

Choice (D) provides a bit more reason to believe that "diallyl sulﬁde repelled the mosquitoes" by showing, in cases of insects on which diallyl sulﬁde has no repellent effect, there was no repellent effect.

In other words, since "ﬂooded ﬁelds would normally attract mosquitoes," it stands to reason that SOMETHING repelled mosquitoes. OK, so, since the fields were garlic fields, maybe diallyl sulﬁde repelled mosquitoes.

Then, (D) says, "Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer."

So, whatever repelled mosquitoes did not repel those insects.

That information allows us to eliminate some things that would have repelled a wider spectrum of insects, such as naphthalene or a fuel spill, giving us more reason to believe that it was indeed diallyl sulﬁde and not something else that caused there to be no mosquitoes in the fields.

stackskillz · Answer

Conclusion  - Diallyl sulphide (DS) is the reason that no mosquitoes were found in the flooded garlic ﬁelds.
 Type  - Strengthen

(A)  Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.  - Okay onions may or maynot repel mosquitos, but doesn't tell us about the garlic field situation.  Drop

(B)  The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years  - No impact since, we need to answer why flooded garlic fields had no mosquito. This is actually paradoxical information, since any species with low population would want to increase it's count, so why didn't they use the flooded garlic fields?  Drop

(C)  By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.  - Did the garlic plants get killed with fungi, yes. Did the flooded garlic fields have DS to repel mosquito? Maybe, can't say for sure.  Drop

(D)  Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer  - Confirms our suspicion, that it is indeed DS that caused the mosquitoes from laying eggs.  Keep

(E)  Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.  Good, less mosquitoes, less problems. However, doesn't support the conclusion.  Drop

RenB · Answer

Hi  AjiteshArun   KarishmaB 
The official solution says that E would weaken the argument. I am not able to wrap my head around why it would weaken. Can you please guide?

AjiteshArun · Answer

Hi RenB,

The conclusion is "diallyl sulﬁde from the garlic repelled the mosquitoes". To strengthen this, we could say (for example) that there's nothing else that can repel mosquitoes. That would help us lock diallyl sulﬁde down as the reason.

On the other hand, if the question asked us to weaken the conclusion, the correct option may have introduced an alternative way to repel mosquitoes. That is, there is at least one other thing (apart from diallyl sulﬁde) that can cause the same outcome. That's the basic structure we see in option E.

KarishmaB · Answer

Premises:  
One summer, floods covered garlic ﬁelds. This region had a large mosquito population.
Flooded ﬁelds normally attract mosquitoes, yet no mosquitoes were found in the ﬁelds.
Diallyl sulﬁde, a major component of garlic, is known to repel several species of insects, including mosquitoes.

Conclusion:   It is likely that diallyl sulﬁde from the garlic repelled the mosquitoes.

Our conlcusion is saying that specifically "diallyl sulﬁde" from garlic repelled the mosquitoes.
We need to strengthen that indeed "diallyl sulﬁde" from garlic was the reason. No something else from garlic, not some other plant found in the field etc.

(A) Diallyl sulﬁde is also found in onions but at concentrations lower than in garlic.

Irrelevant.

(B) The mosquito population of the region as a whole was signiﬁcantly smaller during the year in which the ﬂooding took place than it had been in previous years.

Mosquito population was signiﬁcantly smaller but it was still there. Why did the fields not have any?
If anything, it weakens that "diallyl sulﬁde" from garlic was the reason. It seems to suggest that something else had led to reduction in number of mosquitoes.

(C) By the end of the summer, most of the garlic plants in the ﬂooded ﬁelds had been killed by waterborne fungi.

End of the summer is irrelevant. Our point is why there were no mosquitoes in garlic fields during summer when fields got flooded.

(D) Many insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds throughout the summer.

Insect species not repelled by diallyl sulﬁde were found in the ﬂooded garlic ﬁelds. It increases the probability that diallyl sulﬁde was the one responsible because insects not affected by it were found but mosquitoes which are affected by it were not found. Mind you, it just increases the probability that diallyl sulﬁde was responsible. It does not prove that it was.

Take a simple case: Say there was coffee, cake and a sandwich on the table. After a few hours, it was found that the cake was eaten by someone. I know that my brother loves cake but does not like coffee and sandwiches.

Conclusion: My brother ate the cake.

What will strengthen it? If I am told that coffee and sandwiches were left as it is, then it increases the probability that my brother ate the cake. 
This is the same logic.

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

We are talking about garlic fields and what eliminated mosquitoes there. We are not given anything about whether marigolds were there on the field too so this option is irrelevant. 
If it were to have some impact (say with some additional info about marigold presence in surroundings etc), the impact would be that of a weakener. This option suggests that the mosquitoes could have been eliminated by some other toxins, not diallyl sulﬁde.

Answer (D)

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One summer, floods covered low-lying garlic ﬁelds situated in a region

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