Meaning:
1. Researchers studied Brain scans of volunteers
2. Volunteers – pondered ethical dlemmas
3. Researchers found that Basis is emotion not logic or analytical reasoning.


Error Analysis
Researchers
<Ving modifier modifies researchers > studying the brain scans of volunteers (Relative pronoun referring to Volunteer) who pondered ethical dilemmas

Have found
That “basis for making tough moral judgments” (subject – singular) is emotion not logic or analytical

No subject verb error,
No modifier error.

Option A is correct as Is.

Lets do POE to make it sure.

(B) the brain scans of volunteers who pondered ethical dilemmas and found the basis to make tough moral decisions to be
No verb for subject Researchers
Illogical meaning “Volunteers pondered and found”

(C) the brain scans of volunteers pondering ethical dilemmas and found that the basis for making tough moral decisions is
Subject without verb “Researchers Blah blah and Found” part before and does not have any verb

(D) volunteers’ brain scans while pondering ethical dilemmas have found the basis to make tough moral judgments to be
Highly illogical meaning
Researchers while pondering, have found

(E) volunteers’ brain scans while they pondered ethical dilemmas have foundthat the basis for making tough moral judgments is
Incorrect same as option D

Researchers studying the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is emotion, not logic or analytical reasoning.

A) the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is

From my point of view, the meaning of the correct answer (option A) is not totally precise and, hence, the sentence could be improved.

It says "the brain scans of volunteers who pondered ethical dilemmas". Well, everyone (or almost everyone) pondered ethical dilemmas in the past. Hence, this is somehow vague or inconcrete.

The idea would be better expressed if it said something like "the brain scans of volunteers while they pondered ethical dilemmas".

Your thoughts on this idea will be greatly appreciated.

Thank you for your response Abhishek009, but you did not answer to my question.

Abhishek009,

I probably did not put the best example as an alternative to the correct answer, but my intention was to cast some doubt on the logicality of that aspect of the correct answer.

Nonetheless, I agree with you. Among all the options, A is the best.

Thank you so much for your responses.

Brain Scans
 


First glance

Nearly the entire sentence is underlined, so keep an eye out for the Big Four: Structure, Meaning, Modifiers, and Parallelism.

Issues

(1) Structure: studying…and found

Answers (B) and (C) both insert the word and before found, changing the sentence structure. (A), (D), and (E) use the helper verb have before found instead. Which sentence structure is correct?

Researchers studying…

(A) ...the brain scans...have found that the basis...is emotion
(B) …the brain scans…and found the basis…to be emotion
(C) …the brain scans…and found that the basis…is emotion
(D) ...the brain scans...have found the basis...to be emotion
(E) ...the brain scans...have found that the basis...is emotion

Studying the brain scans modifies researchers. In one interpretation of (B) and (C), the core subject and verb are researchers and found. In this case, there should not be an and between the subject and verb (researchers found). Alternatively, the word found could be seen as parallel to pondered: volunteers who pondered…and found. In this case, there is no main verb connected with the subject researchers at all, since all of the verbs are contained within modifiers. Under either interpretation, neither (B) nor (C) is a complete sentence; eliminate both. In (A), (D), and (E), the core subject and verb are researchers have found; this is correct.

(2) Idiom: the basis to make

The answer choices flip back and forth between the basis for making and the basis to make.

The correct idiom is the basis for: the basis for doing X is Y. Eliminate answers (B) and (D).

(3) Topic: Modifier / Meaning: while pondering

Pronoun: while they pondered

The opening structure of each choice changes.

(A) & (B) the brain scans of volunteers who pondered
(C) the brain scans of volunteers pondering
(D) volunteers’ brain scans while pondering
(E) volunteers’ brain scans while they pondered

While it is possible to construct a correct option starting with volunteers’ brain scans, in this case choices (D) and (E) are faulty. In (D), the sentence reads: Researchers studying X while pondering Y. This parallel structure indicates that the researchers were pondering ethical dilemmas, not the volunteers. While it is possible in general for researchers to ponder ethical dilemmas, that isn't what this sentence describes.

Answer (E) reads: Researchers studying volunteers’ brain scans while they pondered ethical dilemmas. In this case, the pronoun is ambiguous. Logically, the volunteers should be the ones pondering. Since both the main subject researchers and the pronoun they are in subject positions, parallelism suggests that they points to the subject researchers.* Between this choice and answer (A), answer (A) is better because the meaning is unambiguous.

The Correct Answer

Correct answer (A) is a complete sentence and unambiguously indicates that the volunteers, not the researchers, are the ones who pondered ethical dilemmas. It also uses the correct idiom the basis for X is Y.
 
*NOTE: the official explanation says that the pronoun they in answer (E) “must” point to researchers. However other official questions have used a subject pronoun to refer to a possessive noun, including the correct answer for #138 in the 2016 Official Guide for GMAT Review / #805 in the 2017 Official Guide. In the case of #138 / #805, no ambiguity exists because only one noun could possibly function as the antecedent. In the case of the Brain Scans problem, the two potential antecedents create the ambiguity.
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Experts:

I am still struggling to comprehend this question.

From the meaning of the sentence, I thought that the researchers where studying the volunteers' brain scans "during the act of them (volunteers) pondering ethical dilemmas" and A does not demonstrate that:

Researchers studying the brain scans of volunteers who pondered ethical dilemmas

Here volunteers may be pondering ethical dilemmas at different times during the day -- not clear that researchers studied them "while" they were pondering dilemmas.

For this reason, I chose D over A.

(D) volunteers’ brain scans while pondering ethical dilemmas have found the basis to make tough moral judgments to be



However, from the responses, I see that "while pondering ethical dilemmas" in D modified researchers and NOT volunteers.
Can someone explain why it (while pondering ethical dilemmas) would not modify volunteers in D?

What if D was written as:

(D) volunteers brain scans while pondering ethical dilemmas have found the basis to make tough moral judgments to be

OR
(D) volunteers’ brain scans who were pondering ethical dilemmas have found the basis to make tough moral judgments to be

Researchers studying the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is emotion, not logic or analytical reasoning.

(A) the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is

(B) the brain scans of volunteers who pondered ethical dilemmas and found the basis to make tough moral decisions to be

(C) the brain scans of volunteers pondering ethical dilemmas and found that the basis for making tough moral decisions is

(D) volunteers’ brain scans while pondering ethical dilemmas have found the basis to make tough moral judgments to be

(E) volunteers’ brain scans while they pondered ethical dilemmas have found that the basis for making tough moral judgments is

Sir,
Could you please explain the deal with possessive pronouns.
I have observed that most of the time, they fall under incorrect answers category.
Please explain their usage in both the scenarios if exists.
Thanks in advance,
Yash

Researchers studying the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is emotion, not logic or analytical reasoning.

(A) the brain scans of volunteers who pondered ethical dilemmas have found that the basis for making tough moral judgments is
(B) the brain scans of volunteers who pondered ethical dilemmas and found the basis to make tough moral decisions to be
(C) the brain scans of volunteers pondering ethical dilemmas and found that the basis for making tough moral decisions is
(D) volunteers’ brain scans while pondering ethical dilemmas have found the basis to make tough moral judgments to be
(E) volunteers’ brain scans while they pondered ethical dilemmas have found that the basis for making tough moral judgments is

Please help correct me if my train of thought is incorrect GMATNinja

It seems like (C) and (D) are saying: Researchers are also pondering, whereas original sentence intend to have the volunteers do the pondering.

In (B), Researchers studying ... and found ... to be. and indicates some sort of parallelism and there is nothing.

In (E), while they pondered ... they referring to Researchers? wrong, researchers are not doing the pondering. they referring to brain scans? wrong; brain scans cannot do the pondering.

So to paraphrase

(C) the brain scans of volunteers pondering ethical dilemmas and found that the basis for making tough moral decisions is Brain Scans of volunteers pondering

what is pondering modifying? - volunteers or Scans
Answer - volunteers

Takeaway :-
so a -ing modifier can infact modify a noun in a preposition phrase [u][/u]

Please keep me honest ...... thanks