Source: Official Guide for the GMAT 13th Ed. Sentence Correction; #112 Official Guide for the GMAT 2015 14th Ed. Sentence Correction; #112


Construction of the Roman Colosseum, which as

Construction of the Roman Colosseum, which as officially known as the Flavian Amphitheater, began in A.D. 60, during the reign of Vespasian, was completed a decade later, during the reign of Titus, who opened the Colosseum with a one-hundred-day cycle of religious pageants, gladiatorial games, and spectacles.

4 Explanations


reema mittal

For option C:As I know " , + and" should also have a subject when a new clause begins while the correct option doesn't mention the subject distinctively. For example the following sentence(similar to the correct option) is considered incorrect on GMAT:
-Jim washed the bedroom, and cleaned the window.
Although for parallelism and is necessary but if a new clause begins it should mention the subject separately? Am I correct?

Nov 25, 2019 • Comment

Adam Lyons, Magoosh Tutor

Hello Reema,
You are correct. However, the comma here is being used in a totally different way: it's not separating two clauses. Rather, the commas before "and" is used with another comma to surround the nonessential information "during the reign of Vespasian." Without that information, we'd drop the comma and have this:
"began in A.D. 69 and was completed a decade later," with no comma before "and." Using your example, this would be okay:
-Jim washed the bedroom, which was filthy, and cleaned the window.
The comma before the "and" works here because it's not separating clauses, but rather surrounding inessential information, a totally different function.
Hope that helps!

Dec 1, 2019 • Reply


Harsh Singh

How are "Began" and "was completed" parallel to each other in Choice C. Should n't we have "Was began" and "was completed" to make parallelism perfect ? Please explain team.

Aug 27, 2017 • Comment


Hi Harsh,

Happy to help :)

The subject is "construction." It is incorrect to say "construction was began," and it is also incorrect to say "construction completed."

The verb "to begin" is an intransitive verb that does not need an object, so we can simply say "construction began."

By contrast, "completed" here is a past participle, not a full verb.

When used as a verb, "complete" must have an object (we could say "the works completed construction" or "construction was completed," but not "construction completed").

Aug 27, 2017 • Reply


Andrew Smith

Could someone please explain the necessity (or lack thereof) of the word "which"?

Oct 15, 2015 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Andrew :)
"Which" is a relative pronoun and, as a noun modifier, will modify the noun it touches. In this sentence, the word "which" is needed to clarify that the Roman Colosseum, and not the construction of the Roman Colosseum, was officially known as the Flavian Amphitheater. "Which" is therefore used correctly in this sense in A and C. From there, and as Mike explains in the video, without the joining word "and" between "began" and "completed," A is incorrect.
Hope this helps!

Nov 7, 2015 • Reply


Gravatar Mike McGarry, Magoosh Tutor

May 25, 2013 • Comment

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