A. The ophthalmologists' offices have begun selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool --- beginning of selling is an one-time affair; Hence, we need a simple past to describe that. Wrong

B. The ophthalmologists' offices began the selling of prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool … began the selling is unidiomatic
C. That ophthalmologists have begun the selling of prescription goggles to their customers once Olympic pool the nearby gymnasium had completed adding ---- 1 a fragment 2. Ophthalmologists have not begun; their offices did. --- Distortion of the original meaning


D. The ophthalmologists began selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool ….. Distorted version. It is the offices that began selling; not the ophthalmologists themselves

E. That ophthalmologists' offices began selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool – best on all counts tense usage and keeping intact the meaning.

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E: Fragment sentence. The 'That' relative clause could constitute a subject. However, the answer choice as a whole is missing a verb.

Past Perfect: We use the past perfect if one action in the past precedes another past action and if we need to clarify the time sequence. In this problem, the earlier past event 'had completed adding...pool' precedes the ophtalmologists' decision to sell prescription googles to their customers. In addition, the past perfect is correctly used to empahsize the order of events.
As a result, we use the past perfect for the earlier past action and a simple past tense verb for the later one. Answers A & C incorrect.

We are left with B and D:
Answer B: Wrong. 'The selling of prescription googles' is redundant in comparison with 'selling prescription googles'. Pure redundancy is always wrong on the GMAT.

Hence, D correct.

You are right. I misread that for the
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but what about meaning distortion? D says ophthalmologists instead of offices; I don't think GMAT will tolerate such a wide distortion.
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The goggles in question are prescribed by the ophtalmologists and sold in their offices not by their offices.

Bumping for review and further discussion*.

*New project from GMAT Club!!! Check HERE

I see a 3/2 split. With A, B and E using a form of "ophthalmologists' offices" selling the goggles. This doesn't make sense and its a bit awkward since the offices are selling the goggles and not the ophthalmologist.

In C, the use of that at the beginning is awkward and unidiomatic. Therefore, we are left with D which is clearer and to the point.

Meaning wise also D looks good. ophthalmologists having customers - is logical. ophthalmologists' offices having customers - doesn't convey proper meaning.

Based on a webinar I attended yesterday, I believe that we have to pick an option which is logically in sync with the original sentence. So, ideally we have to pick an answer choice which is logically similar to the original sentence and is grammatically correct.
Is my above statement correct? If it is, saying that ophthalmologists selling the goggles change the logic of original sentence(which conveys that office is selling goggles).
Option B retains the logic of the original sentence. 'began the selling of' might be a bit verbose but it seems to be grammatically correct. Shouldn't this mean that B is the only option which is both logically in sync with the original sentence and grammatically correct as well?

Could someone please comment on it.

Thanks

The first part (The ophthalmologists' offices began the selling of prescription goggles) looks fine here in option B. In the second part I think 'ophthalmologists' offices having customers' doesn't seem logical. Even in the question its the same. 'ophthalmologists having customers' sounds more better and logical than 'ophthalmologists' offices having customers'. That's why I chose D.

I misread That as The in E and opted E. Now i see why D is right answer .

is the usage of "once" correct in this context?
should once put forward a future statement. eg: he will[ sell the medicine once he gets it.

Shouldn't it be "since" in this context?

The ophthalmologists' offices have begun selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool.

A. The ophthalmologists' offices have begun selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool
B. The ophthalmologists' offices began the selling of prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool
C. That ophthalmologists have begun the selling of prescription goggles to their customers once Olympic pool the nearby gymnasium had completed adding
D. The ophthalmologists began selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool
E. That ophthalmologists' offices began selling prescription goggles to their customers once the nearby gymnasium had completed adding an Olympic size outdoor pool

Explanation: Here we can see a 3/2 split if we want to solve as quickly as possible
One is Opthamalogists' offices vs Opthalmologists
We have a pronoun reference "their customers" in the subsequent line. So, it refers to opthalmologists.
In C & D --> we can go to D because C has issue with have begun & fragment sentence ( once Olympic pool the nearby gymnasium had completed adding)