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Official Explanation

Read the Original Sentence Carefully, Looking for Errors:

The sentence as written contains no errors. The underlined portion consists of just nouns, which are part of a parallel construction. The sentence describes a new invention that can be used "to calculate the pressure ... and to detect the starting and ending points ...." Note that the two parts of this construction are parallel in form. Expect to choose (A), but check the other choices to make sure nothing was overlooked.

Scan and Group the Answer Choices:

A quick vertical scan of the choices reveals a 3-2 split, with (C), (D), and (E) beginning with "where," while (A) and (B) begin with "the." More analysis needs to be done to determine the significance of this split, however.

Eliminate Wrong Answer Choices:

(B) also demonstrates proper parallelism, but it is unnecessarily wordy. Points are by definition at specific locations, so saying that one can detect the locations of the points offers no more information than saying one can detect the points. The GMAT prefers concise wording whenever possible, and (B)'s wordiness offers no advantage over (A)'s conciseness. Eliminate (B).

(C), (D), and (E) all use the non-parallel "to calculate the pressure ... and to detect where X and Y are located." Parallel structure would be either "to calculate the pressure ... and to detect X and Y," as in (A), or to calculate how much pressure ... and to detect where X and Y .... Eliminate these three choices.

As expected, (A) is correct.

TAKEAWAY: Watch out for two-part constructions that require parallelism. They are common but easy to overlook when there are many words between the two parts of the construction.

I prefer A over B because "that" in B refers to strokes, which are not the sentence talking about not detectable via conventional 2D analysis but the starting and ending points of the strokes are not detectable via conventional 2D analysis.

Excellent point.

I think A makes more sense, because the restrictive clause is directly modifying the stokes. Whereas the verb phrase modifies the locations.

Moreover, A has a parallelism between 2 things
to calculate the pressure used
and
to detect the starting and ending points of strokes not detectable.

OE will definetly shed more light.

I understand your take on parallelism.
But I wanted to bring people's attention one thing on modification.
to detect the starting and ending points of strokes not detectable via conventional 2D analysis.
where do you guys think "not detectable via conventional 2D analysis" modifies? Is it modifying strokes or the points?
I think there is a slight shift of meaning between the two.
C and E make pretty unattractive options, but at least they they don't generate a confusion over whether points or strokes are not detectable.
What do you guys think?

I do agree that this is not an error- free question.
There are grave doubts about choice A and for that matter even about B.
1. Addition of a verb ‘are’ isn’t going to be helpful since it is not the strokes that are not detectable but indeed the starting and ending points that are not detectable. But a modifier, not preceded by a comma has to modify its proximate noun, strokes in this case.
A verb is not going to serve any purpose in an infinitive phrase as we have in this example.
B is also wrong, since the inclusion of the locations adds to further muddle as it is now claimable that it is logically the locations that are not detectable rather than the points or the strokes. Of course the puritans will strongly plead that the restrictive pronoun ‘that’ will only have to refer to the ‘strokes’ by virtue of its proximity.
Overall, this question doesn’t seem to give us any take – away at the end. At best, we can tolerate A for its brevity, though with a pinch of salt.

(A) the starting and ending points of strokes Correct
(B) the locations of starting and ending points of strokes that are that are seems to modify strokes, incorrect
(C) where starting and ending points are located, which are Where is not required here, no location mentioned
(D) where starting and ending points are located Where is not required here, no location mentioned
(E) where the starting and ending points are located, which are Where is not required here, no location mentioned

Hi GMATNinja can you please explain why B is incorrect? I chose A but I can't figure out exactly why B is wrong.

Thanks a lot!

Hello Tanya291095,

We hope this finds you well.

To answer your query, Option B is not actually incorrect; it is just far wordier than it needs to be, making Option A the superior answer choice.

We hope this helps.
All the best!
Experts' Global Team

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