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Question

Difficulty: MediumPunctuation of Nonessential Elements

In 1967, astrophysicist Jocelyn Bell Burnell detected a series of extremely regular radio pulses while analyzing data from a newly constructed radio telescope. These anomalous signals _______ led to the discovery of pulsars, which are rapidly rotating neutron stars that emit beams of electromagnetic radiation. Burnell’s groundbreaking work revolutionized our understanding of the universe, earning a place among the most significant astronomical breakthroughs of the twentieth century.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. A
    , which were initially nicknamed 'Little Green Men' due to their unexpected regularity—
  2. —which were initially nicknamed 'Little Green Men' due to their unexpected regularity—Answer
  3. C
    —which were initially nicknamed 'Little Green Men' due to their unexpected regularity,
  4. D
    which were initially nicknamed 'Little Green Men' due to their unexpected regularity—

Answer

The choice that uses matching em dashes to set off the nonessential clause: '—which were initially nicknamed 'Little Green Men' due to their unexpected regularity—'.
The correct choice properly sets off the nonessential relative clause with matching em dashes at both the beginning and the end. In Standard English conventions, a nonessential parenthetical element must be enclosed by matching punctuation marks: two commas, two em dashes, or two parentheses.

Step-by-Step Solution

1
Identify the nonessential element in the sentence.
The clause 'which were initially nicknamed 'Little Green Men' due to their unexpected regularity' is nonessential because the main sentence ('These anomalous signals led to the discovery of pulsars') remains grammatically complete and retains its core meaning without it.
Nonessential elements must be set off from the main clause using matching punctuation.
2
Determine the correct punctuation pattern to set off the nonessential clause.
The punctuation marks at the beginning and end of the nonessential clause must match (either two commas, two em dashes, or two parentheses).
Using different punctuation marks (such as a comma at the beginning and an em dash at the end) violates the rule of punctuation symmetry for nonessential elements.
3
Evaluate the choices to find the one that uses matching punctuation.
The choice that begins with an em dash and ends with an em dash is correct, while the others use asymmetrical punctuation or omit the opening punctuation mark.
This ensures grammatical consistency and adheres to Standard English conventions.

Key Concept

Punctuation of Nonessential Elements
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Topics

Punctuation of Nonessential Elements

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