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Difficulty: MediumCommas with Nonessential and Parenthetical Elements

The following passage contains an underlined portion.

In 1967, astrophysicist Jocelyn Bell Burnell detected a series of anomalous radio signals while analyzing data from a newly constructed radio telescope. These rapid pulses, which recurred every 1.3 seconds, initially baffled researchers who were searching for cosmic sources. The team jokingly dubbed the mysterious source 'Little Green Men 1' before identifying it as a pulsar, a rapidly spinning neutron star.

Which choice best punctuates the underlined portion of the passage?

  1. NO CHANGEAnswer
  2. B
    pulses, which recurred every 1.3 seconds initially
  3. C
    pulses; which recurred every 1.3 seconds, initially
  4. D
    pulses, that recurred every 1.3 seconds, initially

Answer

The correct option is the one that reads 'NO CHANGE', keeping the pair of commas around the nonessential clause 'which recurred every 1.3 seconds'.
The correct choice keeps the original phrasing, which uses a pair of commas to enclose the nonessential relative clause. Because the information about the recurrence interval is parenthetical and not required to identify the pulses, it must be set off with a comma at its beginning and a comma at its end.

Step-by-Step Solution

1
Identify the clause 'which recurred every 1.3 seconds' and determine if it is essential (restrictive) or nonessential (nonrestrictive) to the meaning of the sentence.
The clause is nonessential because removing it ('These rapid pulses initially baffled researchers') does not alter the fundamental meaning or identity of the pulses.
Nonessential information must be set off from the rest of the sentence using punctuation marks like commas.
2
Select the correct punctuation to set off this nonessential clause.
A pair of commas is required, one at the beginning of the clause (after 'pulses') and one at the end of the clause (after 'seconds').
Omitting one of the commas or using a semicolon creates grammatical errors, while using 'that' with commas incorrectly treats a restrictive pronoun as nonessential.

Key Concept

Commas with Nonessential and Parenthetical Elements
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Topics

Commas with Nonessential and Parenthetical Elements

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