Augustus Caesar is known to have commissioned the Pantheon a monument

OFFICIAL EXPLANATION


THE PROMPT

• If this sentence seems too long to follow, strip the sentence.

→ Remove the non-essential phrase a monument to all the deities of Rome and shorten the last part to aftermath of XYZ.

→ The sentence, stripped, now states:
Augustus Caesar is known to have commissioned the Pantheon . . . as part of a construction program undertaken in the aftermath of XYZ.

THE OPTIONS
• This option looks promising

• The sentence is obviously talking about events in the past.

•The sentence is also asserting that in the present, a certain fact about Augustus Caesar is generally "known."

• We need a verb tense that captures both the past and present aspects of the assertion.

→ The construction is known to have commissioned is a very good way to refer to current knowledge about past events.

• Do not worry about passive voice.

→ In fact, passive voice is often better than active voice to describe general knowledge claims because

(1) we want to emphasize the fact about Caesar rather than who knows that fact, and the passive construction allows us to avoid any mention of the "knowers"; and

(2) in English, we use passive voice when we do not know or care about who the agents are (agents = the people who know).

• you might want to check the material we stripped (not the material we summarized, which is in the non-underlined portion)

→ the non-essential clause contains an appositive that correctly uses the noun a monument to all the deities of Rome to refer back to the Pantheon.
(If you are not sure about (A), keep it tentatively and look for a better answer.)
ELIMINATE A

• What happened to the verb? This option is a nonsensical fragment.

• The verb was should be placed where I have indicated.

• the verb tense in "is known to have been commissioned" is correct. See Notes, below.
ELIMINATE B
• We have another nonsensical fragment without a verb.

• The who "steals" the only verb, commissioned.

• Using a relative clause (a who- or that-clause) and omitting a main verb is a common GMAC trap, especially in sentences that are long or that have long nonunderlined parts.
ELIMINATE C

• What was a monument to all the deities of Rome? Not Augustus Caesar.
→ When a noun modifier is too far from its noun, we have a misplaced modifier or a dangling modifier.

→ GMAC loves to test introductory modifiers, too.

→ Pay attention to introductory phrases.

Do they modify a noun?

If so, see whether those intro phrases modify the correct noun.

→ In this case, the intro phrase is an appositive (a noun + noun modifiers phrase) that re-describes or gives "bonus" information about another noun. That noun is the Pantheon.

• An introductory phrase that is an appositive must modify the subject of the immediately following clause.
→ Almost always, that subject is placed right after the comma.
(On rare occasions, a short phrase may intervene between the comma and the targeted subject, but the clause containing the subject is still placed right after the appositive.)

• After we read the words [a] monument to all the deities of Rome, in other words, the next thing we should be reading about is the Pantheon, not Augustus Caesar.
ELIMINATE D
• we need the word undertaken (the past participle) rather than undertaking (present participle)

→ We are reading about a project [that was] undertaken by Augustus Caeasar.

-- For those of you who like to know terminology, the adjective undertaken is a "reduced relative clause."
-- From the relative clause that was undertaken [by...] we "reduce" the clause by removing the to be verb (was) and the word that. We keep only the adjective undertaken.

→ undertaking sounds silly and is illogical.
-- undertaking suggests that the project itself was initiating an activity.
ELIMINATE E

The best answer is A.

Notes

• you should understand that the construction is known to have Xed (verbED) means that we know something now, in the present, about events that happened in the past.

"Is known" sounds somewhat authoritative: whatever "it is known" refers to is generally accepted as truth.
→ Correct Augustus Caesar is known to have commissioned the Pantheon.
-- "Known to have commissioned" describes Caesar and is the subject complement on the other side of the linking verb is.

→ The verb tense in (B) is similar to what I wrote immediately above and is correct.
-- Known to have been commissioned bydescribes the Pantheon and is the subject complement on the other side of the linking verb is.
→ Correct: The Pantheon is known to have been commissioned by Caesar.

In other words, no verb tense problem exists in B, although it would be easy to believe so.

COMMENTS

VERBAL1 , welcome to SC Butler.
[I'm pretty good at remembering names, and I thought I'd welcomed you before, but if not, boo on me and double welcome to you.)

These answers range from good to excellent.
Nice work, everyone.