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Difficulty: MediumCommas with Nonessential and Parenthetical Elements

Early mariners relied on the astrolabe, a handheld instrument that calculated latitude by measuring the sun's angle. Navigators who sailed across the Atlantic, which could be unpredictable used the device to chart their courses. By the sixteenth century, this tool had transformed maritime exploration.

Which choice is the correct punctuation for the underlined portion of the passage?

  1. A
    NO CHANGE
  2. B
    , who sailed across the Atlantic, which could be unpredictable,
  3. who sailed across the Atlantic, which could be unpredictable,Answer
  4. D
    who sailed across the Atlantic; which could be unpredictable,

Answer

who sailed across the Atlantic, which could be unpredictable,
The correct answer properly leaves the restrictive clause 'who sailed across the Atlantic' unpunctuated while using a pair of commas to set off the nonessential relative clause 'which could be unpredictable'. This ensures that the subject 'Navigators' is directly connected to its modifier, and the extra parenthetical information is correctly separated from the main sentence structure.

Step-by-Step Solution

1
Identify the clauses in the underlined portion and determine whether they are restrictive (essential) or nonessential (parenthetical).
The clause 'who sailed across the Atlantic' is restrictive because it defines which specific navigators used the device. The clause 'which could be unpredictable' is nonessential because it adds extra information about the Atlantic but is not necessary to identify the ocean.
Restrictive clauses do not receive commas, while nonessential clauses must be enclosed in a pair of commas.
2
Evaluate the punctuation needed for both clauses.
No commas should surround 'who sailed across the Atlantic'. A comma must precede 'which' and another comma must follow 'unpredictable' to close the nonessential clause.
This maintains the grammatical separation of parenthetical information without interrupting the relationship between the subject 'Navigators' and its modifier.

Key Concept

Distinguishing between restrictive and nonessential clauses to apply correct comma punctuation.
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Topics

Commas with Nonessential and Parenthetical Elements

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