Under laboratory conditions, fruit flies can learn to respond to odors

Question

Under laboratory conditions, fruit flies can learn to respond to odors that elicit no response from them in nature. Mutant fruit flies that cannot produce a certain enzyme are, however, incapable of such learning. These mutant flies respond to other odors just as ordinary fruit flies do. Thus it is unlikely that the enzyme's absence impairs fruit flies' perception of odors since, presumably,  fruit flies would not have an enzyme that was needed only for the perception of odors that fruit flies do not respond to in nature . Instead, what the enzyme's absence probably impairs is the fruit flies' ability to learn, since  many researchers believe that this enzyme is somehow involved in the process of forming memories .

In the argument given, the two  boldfaced  portions play which of the following roles?

A. The first is evidence that has been used to corroborate a judgment that the argument contends is false; the second is that judgment.
B. The first is a hypothesis that the argument opposes; the second is a judgment that has been advanced in support of that hypothesis.
C. The first is the hypothesis that the argument as a whole seeks to establish; the second provides support for that hypothesis.
D. The first presents an explicit assumption that is introduced in arguing for the position that the argument adopts; the second provides evidence to support that position.
E. The first offers justification for an assumption that is explicitly made in the argument; the second states that assumption.

MartyTargetTestPrep · Accepted Answer

Under laboratory conditions, fruit flies can learn to respond to odors that elicit no response from them in nature. Mutant fruit flies that cannot produce a certain enzyme are, however, incapable of such learning. These mutant flies respond to other odors just as ordinary fruit flies do. Thus it is unlikely that the enzyme's absence impairs fruit flies' perception of odors since, presumably,  fruit flies would not have an enzyme that was needed only for the perception of odors that fruit flies do not respond to in nature . Instead, what the enzyme's absence probably impairs is the fruit flies' ability to learn, since  many researchers believe that this enzyme is somehow involved in the process of forming memories .

A. The first is evidence that has been used to corroborate a judgment that the argument contends is false; the second is that judgment.

The author uses the first boldface to support "it is unlikely that the enzyme's absence impairs fruit flies' perception of odors," which is a position of the author, not "a judgment that the argument contends is false." So, the first part of this choice is incorrect.

The second boldface is evidence the author uses to support the author's position "what the enzyme's absence probably impairs is the fruit flies' ability to learn." Thus, the second boldface is evidence the author agrees with, not "a judgment that the argument contends is false." So, the second part of this choice is incorrect.

Eliminate.

B. The first is a hypothesis that the argument opposes; the second is a judgment that has been advanced in support of that hypothesis.

The author uses the first boldface to support "it is unlikely that the enzyme's absence impairs fruit flies' perception of odors," which is a position of the author. Thus, the author agrees with rather than "opposes the first." So, the first part of this choice is incorrect.

The second boldface is evidence the author uses to support the author's position "what the enzyme's absence probably impairs is the fruit flies' ability to learn." So, the second boldface is evidence the author agrees with, not "a judgment that has been advance in support of" "a hypothesis that the argument opposes." So, the second part of this choice is incorrect.

Eliminate.

C. The first is the hypothesis that the argument as a whole seeks to establish; the second provides support for that hypothesis.

This choice at least goes in the right direction since the author does agree with the statements in boldface.

However, the first boldface is not a "hypothesis that the argument as a whole seeks to establish." Rather, it's evidence the author uses to support the author's position "it is unlikely that the enzyme's absence impairs fruit flies' perception of odors."

Also, while the author does use the second boldface for support, it supports the author's position "what the enzyme's absence probably impairs is the fruit flies' ability to learn" rather than the first boldface.

So, both parts of this choice are incorrect.

Eliminate.

D. The first presents an explicit assumption that is introduced in arguing for the position that the argument adopts; the second provides evidence to support that position.

Notice that what this choice fundamentally says is that the first and second boldfaced portions support the author's position.

The first boldfaced portion supports "it is unlikely that the enzyme's absence impairs fruit flies' perception of odors."

The second boldfaced portion supports ""what the enzyme's absence probably impairs is the fruit flies' ability to learn."

Those two supported statements are the author's position.

So, this choice is looking good.

The only other thing we need to confirm is that the first boldface portion can be characterized as "an explicit assumption that is introduced in arguing for the position that the argument adopts."

Notice that the first boldfaced portion is introduced by "presumably." Thus, the first boldfaced portion is indeed something that the author feels can be presumed, meaning, basically, assumed, in arriving at the conclusion.

So, both parts of this choice are correct.

E. The first offers justification for an assumption that is explicitly made in the argument; the second states that assumption.

This choice at least goes in the right direction since the author does agree with the statements in boldface.

However, the first boldface does not support "an assumption that is explicitly made in the argument." Rather, it supports the author's position "it is unlikely that the enzyme's absence impairs fruit flies' perception of odors."

The second part of this choice is also incorrect because the second boldface is not supported by the first.

Eliminate.

Answer: (D)

Elite097 · Answer

MartyTargetTestPrep how is the second boldface an evidence ? That is something the scientists believe so how is it an evidence . Even the author has just written someone s belief so what makes it qualified to be an evidence and FOR what exactly ?

Posted from my mobile device

Posted from my mobile device

mmdfl · Answer

Evidence = facts, statistics, expert opinions, examples, and other information that support the premises of the argument

Fish181 · Answer

The first boldface is clearly an assumption that is stated out loud (look at the word "presumably" before it). The second boldface is definitely evidence or support. Look at the trigger word "since" before it.

Yes2GMAT · Answer

Elite097  I guess some arguments have fallacy in them. We are only asked to find the roles of the boldface portion. To me the whole passage felt like circular reasoning. So, I ended up choosing E as the option because it was hard to differentiate between premise/assumption and conclusion. However, that doesn't mean the author doesn't use the second bold face as a premise.

tommychudw · Answer

To be clear, "believe" or an expert's belief with no rationale given can constitute evidence? Seems ambiguous to me.

For the record, I cancelled D while attempting because of this..

PeachSnapple1 · Answer

Imagine you encounter this as your first question on the GMAT Mock Test - what's up with these fruit flies and the convoluted wordings? Anyway, here's my dumbed-down breakdown of the logic of this question, for my own sake.

Full meaning of the prompt:  Apparently, flies don't respond to odors in nature (I'm gonna take an example of pizza for fun), but they can learn that skill, i.e., responding to the smell of pizza.
Now, some mutant flies cannot produce a certain enzyme (I'll call the Pizza Enzyme). These mutant flies, therefore, can never learn what a pizza smells like. But for other smells besides a pizza, mutant flies and normal flies behave the same way.
Here, the author states the main conclusion   Bruh, what does that conditional double negative phrase   even mean?
After rereading it for like 3 times, in its original wording, it translates into   So, it simply means, if flies have an enzyme, then that enzyme will serve more purposes than just helping the flies know what a pizza smells like. It will do more jobs - specifically, in this question, it's believed that the Pizza Enzyme will help normal flies form memories (and thus, learn). Therefore, the author believes that not having the Pizza enzyme will prevent flies from forming memories/learn.

TLDR:  Mutant flies that lack a certain enzyme cannot learn how to respond to odors. Is it because those mutant flies don't have that special enzyme? Or is it something else? Turns out that that special enzyme helps flies form memories (and thus the ability to learn), and has nothing to do with the perception of odors or whatever. 
 TLDR2:  Fact 1 + Fact 2 + Fact 3 --> Main conclusion: It's unlike that X causes Y, because      . In other words, X causes Z, because    .

So, BF1 is the assumption of the author (although I have to admit that rarely in the GMAT do I see a correct answer explicitly states  , as it's well known in the GMAT that the assumption is never written out, because it's an assumption, duh...). BF2 supports the point of the author.

Hence D.

KarishmaB · Answer

Break down the argument:

Under laboratory conditions, fruit flies can learn to respond to odors that elicit no response from them in nature.
Mutant fruit flies that cannot produce a certain enzyme are, however, incapable of such learning. (so either they cannot perceive the odor or cannot memorize what the odor is or cannot respond)
These mutant flies respond to other odors just as ordinary fruit flies do. (they do perceive ordinary odors and respond to them)
Presumably, fruit flies would not have an enzyme that was needed only for the perception of odors that fruit flies do not respond to in nature. (an assumption. Why would the body create an enzyme to perceive only a specific odor which is not present in their usual life?)

Intermediate Conclusion: It is unlikely that the enzyme's absence impairs fruit flies' perception of odors (so even without the enzyme they likely do perception that special odor)

many researchers believe that this enzyme is somehow involved in the process of forming memories. (Researchers believe that the enzyme is required to learn, to memorize the odor)

Main Conclusion: Instead, what the enzyme's absence probably impairs is the fruit flies' ability to learn

BF1 is an explicit assumption of the researchers and in fact it is given as such - the word presumably has been used.
BF2 supports the main conclusion and hence it is called evidence. A statement that supports another statement is evidence.

Hence option (D) works:
D. The first presents an explicit assumption that is introduced in arguing for the position that the argument adopts; the second provides evidence to support that position.

Both statements argue FOR the position of the argument, the main conclusion.

Don't forget: You cannot rely on surface meanings - look for the logical role.

Answer (D)

Now try this boldface question: https://youtu.be/0XVVkCCaEoE

nbharti · Answer

Thanks. It was really helpful.

Dream009 · Answer

I couldn't eliminate b/w C&D

Sajjad1994 · Answer

This explanation  might help!

Goldenfuture · Answer

Its the word presumably - that should make you go in favour of D

Under laboratory conditions, fruit flies can learn to respond to odors

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

Under laboratory conditions, fruit flies can learn to respond to odors

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards