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Question

Difficulty: HardPunctuation of Nonessential Elements

The passage below contains a blank indicating a missing punctuation mark. Which punctuation mark should be placed in the blank to correctly set off the nonessential element?

Answer:Although many historians attribute the invention of the marine chronometer solely to John Harrison, the contribution of his son William—who made several arduous voyages across the Atlantic to test the device's accuracy under harsh maritime conditions【—】was equally vital to solving the long-standing longitude problem. William's meticulous record-keeping helped prove the reliability of the marine chronometer to the Board of Longitude.

Answer

An em dash (—)
The sentence sets off the nonessential relative clause describing William's voyages with an em dash after his name ('William—'). To maintain grammatical symmetry, the clause must also end with a matching em dash. Therefore, an em dash (—) is required in the blank.

Step-by-Step Solution

1
Identify the nonessential element in the sentence.
The phrase 'who made several arduous voyages across the Atlantic to test the device's accuracy under harsh maritime conditions' is a nonessential relative clause modifying the noun 'William.'
This clause provides descriptive information about William but is not grammatically necessary for the main clause to function.
2
Analyze the punctuation starting the nonessential element.
An em dash (—) is used immediately before the relative clause starts, right after the name 'William.'
Nonessential elements must be set off by matching punctuation on both sides to maintain parallel structure.
3
Select the matching punctuation to close the nonessential element.
An em dash (—) must be placed in the blank.
Ending the clause with a comma or any other punctuation mark would create asymmetry with the opening em dash.

Key Concept

Punctuation of Nonessential Elements
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Topics

Punctuation of Nonessential Elements

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