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Difficulty: Very hardCommas with Lists, Clauses, and Coordinate Adjectives

While mapping the outer edges of the galaxy, the astrophysicists recorded several highly, unusual, rapidly pulsating, signals; and they immediately cross-referenced the coordinates with existing stellar databases.

Which of the following is the best choice for the underlined portion?

  1. A
    highly, unusual, rapidly pulsating, signals; and they immediately cross-referenced
  2. highly unusual, rapidly pulsating signals, and they immediately cross-referencedAnswer
  3. C
    highly unusual, rapidly pulsating signals; immediately cross-referenced
  4. D
    highly unusual, rapidly pulsating signals, they immediately cross-referenced

Answer

highly unusual, rapidly pulsating signals, and they immediately cross-referenced
The correct answer properly handles both the adjective punctuation and the clause coordination. In the noun phrase, 'highly' and 'rapidly' are adverbs that modify the adjacent adjectives ('unusual' and 'pulsating'), so no commas should separate them. The coordinate adjective phrases 'highly unusual' and 'rapidly pulsating' must be separated by a comma, but no comma should separate the final adjective 'pulsating' from the noun 'signals'. At the clause boundary, a comma followed by the coordinating conjunction 'and' is correctly used to join the two independent clauses.

Step-by-Step Solution

1
Analyze the punctuation within the adjective phrase modifying the noun 'signals'.
Identify that 'highly' and 'rapidly' are adverbs modifying the adjectives 'unusual' and 'pulsating'. No commas should separate an adverb from the adjective it modifies. The phrases 'highly unusual' and 'rapidly pulsating' act as coordinate adjectives modifying 'signals', meaning they require a comma between them, but no comma should be placed between the final adjective 'pulsating' and the noun 'signals'.
To ensure modifiers and coordinate adjectives are punctuated correctly.
2
Identify the clause boundary and the nature of the clauses.
The sentence contains two clauses: 'the astrophysicists recorded several...' and 'they immediately cross-referenced...'. Both can stand alone as independent sentences.
To determine the appropriate punctuation and conjunctions needed to join the clauses.
3
Determine the correct punctuation to join the two independent clauses.
The clauses must be joined using either a semicolon or a comma followed by a coordinating conjunction (such as 'and'). A comma followed by 'and' is the grammatically correct choice here.
To avoid a comma splice or run-on sentence.

Key Concept

Punctuation of coordinate adjectives and coordination of independent clauses
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Topics

Commas with Lists, Clauses, and Coordinate Adjectives

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