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Difficulty: EasyCommas with Nonessential and Parenthetical Elements

In 1609, Galileo Galilei constructed an instrument that would revolutionize astronomy. The telescope that Galileo built, which had a magnification of three times, helped him discover the four largest moons of Jupiter. These observations challenged the geocentric model of the universe.

Which choice best punctuates the underlined portion of the sentence?

  1. NO CHANGEAnswer
  2. B
    that Galileo built, which had a magnification of three times helped
  3. C
    , that Galileo built, which had a magnification of three times, helped
  4. D
    that Galileo built; which had a magnification of three times, helped

Answer

The correct option is the one that leaves the sentence unchanged: 'that Galileo built, which had a magnification of three times, helped'.
The correct answer keeps the original punctuation. The clause 'that Galileo built' is restrictive because it is essential to identifying which telescope is being discussed, so it should not be preceded by a comma. The clause 'which had a magnification of three times' is nonrestrictive because it provides extra, nonessential details about the telescope, and therefore it must be set off with a pair of commas: one before 'which' and one after 'times'.

Step-by-Step Solution

1
Analyze the role of each clause in the underlined portion of the sentence.
The clause 'that Galileo built' is restrictive (essential to identify which telescope), and the clause 'which had a magnification of three times' is nonrestrictive (adds nonessential details).
Restrictive clauses must not be set off by commas, whereas nonrestrictive clauses must be set off by commas.
2
Verify the punctuation around each clause.
The restrictive clause should have no preceding comma, and the nonrestrictive clause must start and end with commas (before 'which' and after 'times').
This maintains the correct distinction between essential and nonessential information in the sentence.

Key Concept

Commas with Nonessential and Parenthetical Elements
Estimated Time:45s
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Topics

Commas with Nonessential and Parenthetical Elements

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