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Difficulty: HardPunctuation of Nonessential Elements

In 1901, sponge divers recovering artifacts from a shipwreck near the Greek island of Antikythera salvaged a heavily corroded bronze device containing dozens of interlocking gearwheels. Modern historians believe the mechanism was a sophisticated astronomical calculator. The device_______could predict the positions of the sun, moon, and planets decades into the future.

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

  1. A
    —which was capable of tracking complex celestial cycles,
  2. B
    , which was capable of tracking complex celestial cycles—
  3. —which was capable of tracking complex celestial cycles—Answer
  4. D
    which was capable of tracking complex celestial cycles,

Answer

The option containing '—which was capable of tracking complex celestial cycles—' is correct because it sets off the nonessential relative clause with matching em dashes.
The correct answer correctly uses matching em dashes to enclose the nonessential relative clause. Nonessential relative clauses must be separated from the main clause by matching punctuation marks, such as a pair of commas or a pair of em dashes.

Step-by-Step Solution

1
Identify the nonessential relative clause in the sentence.
The clause 'which was capable of tracking complex celestial cycles' is nonessential because the main clause remains grammatically complete and retains its core meaning without it.
Nonessential elements must be set off from the rest of the sentence with punctuation.
2
Check for punctuation consistency around the nonessential clause.
Standard English conventions require that punctuation setting off a nonessential element must be symmetrical (two commas, two parentheses, or two em dashes). Only one option uses matching em dashes to open and close the clause.
Mixing punctuation marks, such as a comma and an em dash, violates grammatical conventions.

Key Concept

Punctuation of Nonessential Elements
Estimated Time:1m 0s
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Topics

Punctuation of Nonessential Elements

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