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Question

Difficulty: MediumPunctuation of Nonessential Elements

The giant squid (*Architeuthis dux*) has long captivated researchers, but its deep-sea habitat makes direct observation extremely difficult. In 2004, Japanese marine biologists captured the first active images of a live giant squid in its natural environment. This historic achievement ______ helped scientists understand the predatory behaviors of this elusive creature.

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

  1. A
    , which occurred off the coast of the Ogasawara Islands—
  2. B
    —which occurred off the coast of the Ogasawara Islands,
  3. —which occurred off the coast of the Ogasawara Islands—Answer
  4. D
    which occurred off the coast of the Ogasawara Islands

Answer

The correct answer is the choice that uses matching em dashes to set off the nonessential relative clause.
The correct choice uses a matching pair of em dashes to set off the nonessential relative clause 'which occurred off the coast of the Ogasawara Islands' from the rest of the sentence. Nonessential elements must be set off from the main clause by matching punctuation marks: either two commas, two em dashes, or two parentheses.

Step-by-Step Solution

1
Identify the nonessential element in the sentence.
The relative clause 'which occurred off the coast of the Ogasawara Islands' adds descriptive detail but is not essential to the main grammatical structure of the sentence.
This helps determine that the clause must be punctuated as a nonessential element.
2
Apply the punctuation rules for nonessential elements.
Nonessential elements must be set off by a matching pair of punctuation marks, such as two commas, two em dashes, or parentheses.
This establishes the criteria for evaluating the punctuation in each option.
3
Evaluate the choices for punctuation symmetry.
Only the option using matching em dashes correctly isolates the clause, whereas other options use mismatched punctuation or no punctuation.
This identifies the grammatically correct option.

Key Concept

Punctuation of nonessential elements
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Topics

Punctuation of Nonessential Elements

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