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Difficulty: HardPunctuation of Nonessential Elements

The following passage is missing a punctuation mark. Read the passage and write the single punctuation mark that correctly completes the sentence by setting off the nonessential element.

Answer:In 1895, Harvard physics professor Wallace Clement Sabine was tasked with improving the abysmal acoustics of the newly constructed Fogg Art Museum lecture hall. Sabine realized that the duration of sound persistence【,】 a metric he later defined as reverberation time, was directly proportional to the room's volume and inversely proportional to its absorptive surfaces.

Answer

A comma (,)
The correct answer is a comma. The nonessential appositive phrase 'a metric he later defined as reverberation time' is closed with a comma after 'time'. To maintain punctuation symmetry, the phrase must also be opened with a comma.

Step-by-Step Solution

1
Identify the nonessential appositive phrase in the target sentence.
The phrase 'a metric he later defined as reverberation time' is a nonessential appositive that renames and describes the noun phrase 'duration of sound persistence'.
Recognizing the boundaries of the nonessential element is necessary to determine where punctuation is required.
2
Locate the punctuation mark used at the closing boundary of the nonessential phrase.
A comma is used after the word 'time' to close the nonessential phrase.
Nonessential elements must be set off with matching punctuation on both sides to maintain structural symmetry.
3
Select the punctuation mark that matches the closing punctuation.
A comma must be placed in the blank to open the nonessential phrase.
Using any other punctuation mark, such as a dash or parenthesis, would result in mismatched punctuation (asymmetry), which is grammatically incorrect.

Key Concept

Punctuation of Nonessential Elements
Estimated Time:1m 30s
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Topics

Punctuation of Nonessential Elements

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