OFFICIAL EXPLANATION

Hi all, I have to post early tonight.
I will hide the answer under the spoiler, which I will remove tomorrow (my tomorrow).





HIGHLIGHTS

• Meaning?
Ernest Hemingway and his writer friends were revered (admired by others) because they wrote about the sense of aimlessness felt by members of the Lost Generation. One of Hemingway's contemporaries was his rival (probably Faulkner or Fitzgerald).

• Structure?
This sentence is slightly deceptive because the compound subject Hemingway and his contemporaries is followed by "one of whom."
A dependent clause such as one of whom... that comes between a subject and verb does not affect the subject's singularity or plurality.
-- one of whom is a dependent clause (it cannot stand on its own as a sentence)
-- one of whom is not an essential modifier (one way to tell? the whole clause is set off by commas).
-- strip the sentence

Ernest Hemingway and his contemporaries, one of whom was known to be a rival of the author, was revered for describing the sense of aimlessness felt by members of the Lost Generation.

Ernest Hemingway and his contemporaries, one of whom was known to be a rival of the author, was [?] revered for describing the sense of aimlessness felt by members of the Lost Generation.

The sentence, stripped:
Ernest Hemingway and his contemporaries [was?] revered for describing the Lost Generation.

• Split #1: Subject verb agreement

The compound subject Ernest Hemingway and his contemporaries is not altered in number by the clause "one of whom."

The plural subject requires the plural verb were [revered].

Eliminate A, B, and D, all of which use the singular verb WAS.

• Split #2: pronoun / antecedent disagreement

Option C uses his ability. That pronoun should be THEIR in order to agree with the compound subject.
Eliminate C

By POE, Answer E is correct

OTHER ISSUES

• WHO/WHOM

Prepositions take objects.
In "one of," the word OF is a preposition. It needs an object. So we use the object pronoun, whom.

A mnemonic to remember WHO v WHOM.
If you see a preposition, use an easy preposition and a singular male person.
Give the present TO ____ HE/HIM?
Give the present TO hiM.
Him ends in M. So does whoM. Use whoM.

Object pronouns: me, you, her, him, it, us, them, whom
Subject pronouns: I, you, he, she, it, we, they, who

Options B and D incorrectly use one of WHO

• TO DESCRIBE / FOR DESCRIBING
This issue is idiomatic.

A person is appreciated (revered) by others FOR describing something well.
A person is not revered by others TO describe something well.
A person might herself be excited TO describe something well . . but she would not herself be revered by others TO describe something. (That sentence is so incoherent that I can barely write it. )

Options B and C are incorrect.

• had been in option C?
HAD + past participle = past perfect, aka the past of the past
To use past perfect (to express the past of the PAST), we first need a past.
We must have at least one event rendered in simole past tense or a time marker that does the same thing as a past tense verb -- namely, that marks of a discrete (non-continuous) point in time in the past.

Option C has neither a simple past tense verb not a time marker. No reason exists to use past perfect.

COMMENTS

Arvind42 , Annet1524 , Xylan (pistachios, and the quote is indeed beautiful ) , J2S2019 , exc4libur , and amitanshumaity , I thought I'd name you all so that you would peek under the spoiler and see: I appreciate your consistent and consistently good replies.

I know. This one was fairly simple. Basics are important.
Happy kudos!

Ernest Hemingway and his contemporaries, one of whom was known to be a rival of the author, was revered for describing the sense of aimlessness felt by members of the Lost Generation.
1st split - to describe/for describing - according to meaning of the sentense B, C, - out
2nd split - was revered/ were revered - should be plural because we have subject: Ernest Hemingway and his contemporaries - A,B,D -out
3d split - who/whom - should be whom one of whom
So, the answer is E

IMO correct answer is E

Ernest Hemingway and his contemporaries, one of whom was known to be a rival of the author, was revered for describing the sense of aimlessness felt by members of the Lost Generation.

A) whom was known to be a rival of the author, was revered for describing - "Ernest Hemingway and his contemporaries" - Plural subject requires plural verb - use of "was" is incorrect.

B) who was known to be a rival of the author, was revered to describe - SVA error;same as A; also use of whom is correct as Objective pronoun is required to show the correct intent of the sentence, receiving the action.

C) whom was known to be a rival of the author, had been revered for his ability to describe - Use of Past perfect tense is not required as not two past events are shown time-shifted here.

D) who was known for being a rival of the author, was revered for describing - SVA error;same as A; also use of whom is correct as Objective pronoun is required to show the correct intent of the sentence, receiving the action.


E) whom was known to be a rival of the author, were revered for describing - Correct

Ernest Hemingway and his contemporaries, one of whom was known to be a rival of the author, was revered for describing the sense of aimlessness felt by members of the Lost Generation.

Structure: X and Y, (Relative Pronoun Modifier) Verb object, verb( S-v agreement error) object.

So, the fatal error here is the S-V agreement. Ernest Hemingway and his contemporaries do not agree in number with 'was revered '.
The modifier is used correctly and the rest of the sentence looks fine.
The choice which corrects this error is E

IMHO E

generis

Thanks a ton for such wonderful wish. Keep posting

Whom should be used to refer to the object of a verb or preposition.
Who should be used to refer to the subject of a sentence.

When in doubt, try this simple trick:

If you can replace the word with “he”' or “'she,” use who.
If you can replace it with “him” or “her,” use whom.