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Difficulty: Very hardPunctuation of Nonessential Elements

Observations from the New Horizons spacecraft have revolutionized our understanding of the Kuiper belt, a region of icy bodies beyond Neptune. Among the most surprising findings is the geological complexity of the dwarf planet Pluto, which [blank] boasts vast plains of nitrogen ice and towering mountains of water ice.

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

  1. —contrary to the expectations of planetary scientists who had predicted a geologically dead world—Answer
  2. B
    , contrary to the expectations of planetary scientists who had predicted a geologically dead world—
  3. C
    —contrary to the expectations of planetary scientists who had predicted a geologically dead world,
  4. D
    contrary to the expectations of planetary scientists who had predicted a geologically dead world,

Answer

The choice that begins and ends the parenthetical phrase with matching em dashes, specifically '—contrary to the expectations of planetary scientists who had predicted a geologically dead world—', is the correct answer.
The correct option uses a matching pair of em dashes ('—contrary to... world—') to set off the nonessential parenthetical phrase that interrupts the relative clause 'which boasts...'. Setting off this parenthetical element symmetrically with either two commas or two em dashes conforms to the rules of Standard English.

Step-by-Step Solution

1
Identify the nonessential element in the sentence.
The phrase 'contrary to the expectations of planetary scientists who had predicted a geologically dead world' acts as an parenthetical insertion modifying the main assertion about Pluto's active features.
Recognizing nonessential elements is necessary to determine where punctuation marks (like commas, em dashes, or parentheses) must be placed.
2
Determine the required punctuation pattern to set off this nonessential element.
Standard English conventions require that nonessential elements be set off by matching pairs of punctuation: either two commas, two em dashes, or two parentheses.
Using mismatched punctuation (such as a comma at the beginning and an em dash at the end) violates the rule of punctuation symmetry.
3
Evaluate the options to find the one with matching punctuation marks.
The option using matching em dashes ('—contrary to... world—') is correct. All other options mix commas and em dashes or omit one of the boundaries.
Selecting the option with symmetrical punctuation ensures the sentence conforms to Standard English conventions.

Key Concept

Punctuation of Nonessential Elements
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Topics

Punctuation of Nonessential Elements

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