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Difficulty: MediumCommas with Lists, Clauses, and Coordinate Adjectives

To reconstruct atmospheric conditions from the last glacial period, glaciologists extracted deep core samples from Greenland's ice sheet, analyzed the trapped, ancient gas bubbles, and recorded precise methane levels.

Which choice for the underlined portion best conforms to the conventions of standard written English?

  1. NO CHANGEAnswer
  2. B
    trapped, ancient gas bubbles; and recorded
  3. C
    trapped, ancient gas bubbles, they recorded
  4. D
    trapped ancient gas bubbles, and recording

Answer

The original phrasing ('NO CHANGE') is correct because 'trapped' and 'ancient' are coordinate adjectives requiring a comma between them, and the list of three parallel verbs is punctuated correctly with commas and a coordinating conjunction.
The original text correctly places a comma between the coordinate adjectives 'trapped' and 'ancient' because both modify 'gas bubbles' independently. Additionally, it preserves parallel structure across the three predicate verbs ('extracted', 'analyzed', and 'recorded') while using a comma before the coordinating conjunction 'and' to separate the elements in the series.

Step-by-Step Solution

1
Analyze the relationship between the adjectives 'trapped' and 'ancient'.
Both adjectives independently describe 'gas bubbles' (you can say 'trapped and ancient gas bubbles' or 'ancient, trapped gas bubbles').
Because they are coordinate adjectives, a comma must separate them.
2
Evaluate the structure of the predicate list in the sentence.
The subject 'glaciologists' performs three actions: 'extracted...', 'analyzed...', and 'recorded...'.
A list of three parallel past-tense verbs requires commas separating the items, including a serial comma before the coordinating conjunction 'and'.
3
Compare the original underlined portion against the alternative choices.
The original text correctly includes the coordinate adjective comma and maintains parallel verb structure with proper list punctuation.
Option A ('NO CHANGE') is the only choice that is grammatically correct and conforms to standard written English.

Key Concept

Commas with Lists, Clauses, and Coordinate Adjectives
Estimated Time:1m 0s
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Topics

Commas with Lists, Clauses, and Coordinate Adjectives

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