In order to improve the aesthetics of the neighborhood a group of

PROCESS OF ELIMINATION
Just after the POE I explain "once outside, twice inside" and collective nouns


• the singular subject group does not agree with the plural verb have
• the idiom, though, is parallel; be is used correctly only "once outside"


• singular group does not agree with plural have
• BE is once outside and once inside.
Because BE comes after not only, BE must also come after but also (BE should be twice inside)


• modifier problem (dangling modifier, misplaced modifier)
The introductory phrase, In order to improve the aesthetics of the neighborhood, describes something that is animate (alive) and conscious (thinking or having intent to improve.)
A park cannot intend to improve anything.
What follows the prepositional phrase should be a group of citizens
• parallelism - the error is identical to that in (B). The second BE (twice inside) is missing.
NOT ONLY BE X BUT ALSO [BE] Y


• BE comes before not only. It should occur only once, outside the idiomatic structure, but BE also comes after but ... also.
Once outside, once inside? Wrong.


Correct.

The answer is E.

CHALLENGE (kudos for answering): in option (D), suppose that I change the placement of BE.
PRETEND option D:
... a group of citizens has suggested that the park not only be cleaned but that it also be beautified
-- Now, is that structure parallel? Why or why not? ("That construction does not follow the idiom" is an assertion, not an explanation.)

HIGHLIGHTS

• how to USE the idiom NOT ONLY X BUT ALSO Y

GMAC tests this idiom frequently. X and Y must be parallel.
I am seeing a lot of misunderstanding about this rule on other threads. No surprise.
Parallelism is hard enough, let alone when coupled with the subjunctive (BE) in an idiomatic construction.

You do not need to know that this structure is called a correlative conjunction, but you do need to know that
1) whatever comes after not only [X] does not "carry over" to the "but also [Y]" part. We have to repeat words.

2) the words "not only" indicate where the parallelism begins. Somewhere before that phrase (usually immediately before), the "root phrase" leads into the parallel structure.
The root phrase in this sentence is
suggested that the park BE or
suggested that the park

3) prepositions, verbs, and split verbs create the most problems. The rule is once outside, twice inside.

I will mark the end of the root and the beginning of the parallel structure with || to show visually what is meant by inside and outside [the idiomatic structure]

Once outside

IF the root is suggested that the park BE as in Option E, then BE is written "outside" the idiom's structure, ONE time.
Correct, BE is ONCE OUTSIDE: . . . suggested that the park be || not only X but also Y
Correct, BE is ONCE OUTSIDE: . . . suggested that the park be || not only cleaned but also beautified

Correct: cleaned and beautified are parallel.
Each works with BE.
Each is a subject complement of the same kind, a past participle (a verbED). Try each one separately.
-- suggested that the park be cleaned (correct)
-- suggested that the park be beautified (correct)

Twice inside

If the root is suggested that the park, as in (B), and we see that BE comes after "not only" or "but also," then BE is already inside the structure once.
But BE must be inside TWO times.
Correct, twice inside: . . . suggested that the park || not only be X but also be Y
Correct, twice inside: . . . suggested that the park || not only be cleaned but also be beautified

How to choose between once outside and twice inside?

If the non-underlined portion contains the word BE and the options offer not only X but also Y, then BE is already outside (before) the idiom. We are stuck with once outside because it comes before "not only." Any option that repeats BE inside is incorrect.

If the question is like this one, we have to decide which underlined portion correctly puts BE either once outside or twice inside.
-- If we see a BE after either [i]not only or but also, then BE is already inside. Now we know that we need to see a second BE after the other part of the idiom. (If BE is inside at all, it must be TWICE inside)
-- If we see a BE before the parallelism marker not only, then that option has already placed the BE outside, and we must see only that one BE. (once outside)

We could use the one-word verb ARE.
-- Once outside, correct: Dancers are not only artists but also athletes.
-- Twice inside, correct:
Dancers not only are artists but also are athletes.
-- Once inside, once outside, WRONG:
Dancers are not only artists but also are athletes.

Although they are not at issue in this sentence, prepositions are tested heavily with idiomatic structures. Same rule: Once outside, twice inside.
-- Once outside, correct: She did pro bono work for not only the Poverty Law Center but also Human Rights Watch.

--Twice inside, correct: She did pro bono work not only for the Poverty Law Center but also for Human Rights Watch.

-- Once outside, once inside, WRONG: She did pro bono work for not only the Poverty Law Center but also for Human Rights Watch.

That last sentence is not likely to strike most people as lacking parallelism. It does lack parallelism. FOR is in the wrong place.
A very good post on this issue, written by Mike McGarry of Magoosh, is HERE.

• collective nouns
When dealing with verb tenses, sometimes people confuse collective nouns with plural nouns.
GROUP is a collective noun that is a singular entity made up of many members. This singular entity takes a singular noun even when followed by a description of members of that group.
A group of citizens? GROUP is singular
A herd of cows? HERD is singular
A flock of birds? FLOCK is singular

A collective noun is a larger category that encompasses multiple items or members.
-- If we have numerous crows, most people would call that group a FLOCK of crows.
-- The correct collective noun for numerous crows is a MURDER of crows.

On the GMAT, collective nouns are singular and take singular verbs.
-- A murder of crows likes to eat all my raspberries.
-- A group of unusual scholars is coming to present at the conference.
Collective nouns in British English often are treated differently. If you speak British English, just be a little careful.

A plural noun does indicate multiple items (or people) but takes a plural verb.
-- Usually we just add -s or -es to the noun and thus plural nouns are not hard to spot.
The cat has green eyes.
The cats have green eyes.
-- Irregular plural nouns include children, people, women, mice, teeth, oxen, cacti
The child has green eyes.
The children have green eyes.

Sometimes the trouble arrives in constructions such as EITHER/OR.
Either the cat or the dogs are in my yard. (Verb matches the nearer subject.)
Either the cat or the murder of crows is in my back yard. [Verb matches the nearer subject, which is singular because it is a collective noun. CROWS is not the subject. "Murder" (flock) is the subject.]

COMMENTS
Wow! Big group. I am thrilled about the Game of Timers competition and now thrilled that it didn't steal my participants.

Kudos to everyone because I got caught between two professional deadlines that were moved up (i.e. in my "real" occupations)— I had to post both this OE and the third set of questions for this week tardily.

techloverforever and longway25 , welcome to SC Butler.

Raxit85 , Xylan , J2S2019 , prashanths , GKomoku , bartk , Arvind42 (thanks for the note!), Archit3110 , Annet1524 , and firas92 - glad to see you all again.

I wanted to give kudos only to answers that explain.
Answers that explain errors—even with two or three words!—are better than answers that simply name errors.
People who do not understand a concept will not be helped by seeing that the concept has a name.
Explaining takes a little more effort and a little (or a lot) more time.

This group is impressive. Almost all of you have written explanations that will help other members who follow.
It's really hard to know what kind of approach will help a person understand. Sometimes a single phrase will trigger an "aha" moment for someone. Many someones, actually.

My favorite part? You already demonstrate part of what B school requires: active, committed learning and teaching.
Nicely done.