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Difficulty: HardRun-on Sentences and Comma Splices

Noctilucent clouds, which are the highest clouds in Earth's atmosphere, form only under extremely cold conditions in the mesosphere. These rare clouds shine bright blue long after sunset because they reflect sunlight from below the horizon. During the summer, temperatures at this altitude drop below minus 130 degrees Celsius, consequently, ice crystals begin to nucleate on meteoric dust particles. Because of their sensitivity to changes in temperature and water vapor, scientists monitor these clouds as early indicators of global climate change.

Which choice, if substituted for the underlined portion, makes the sentence grammatically correct?

  1. A
    NO CHANGE
  2. temperatures at this altitude drop below minus 130 degrees Celsius; consequently, ice crystalsAnswer
  3. C
    temperatures at this altitude drop below minus 130 degrees Celsius, consequently, ice crystals, which
  4. D
    temperatures at this altitude drop below minus 130 degrees Celsius; consequently, because ice crystals

Answer

The correct option uses a semicolon to separate the two independent clauses, followed by a comma after the conjunctive adverb 'consequently'.
The correct option uses a semicolon to separate the two independent clauses, followed by a comma after the conjunctive adverb 'consequently'. This properly resolves the comma splice error without creating any fragment or run-on issues.

Step-by-Step Solution

1
Identify the two main clauses in the sentence surrounding the underlined portion.
The first clause is 'During the summer, temperatures at this altitude drop below minus 130 degrees Celsius' and the second clause is 'ice crystals begin to nucleate on meteoric dust particles.'
Determining where the clauses divide is necessary to evaluate the punctuation and conjunctions needed between them.
2
Analyze the grammatical structure of both clauses to determine if they are independent or dependent.
Both clauses contain a subject and a verb and express a complete thought, meaning they are both independent clauses.
Two independent clauses cannot be joined with just a comma and a transition word (such as 'consequently'), which would result in a comma splice.
3
Evaluate the punctuation and conjunctions in the choices to find the one that correctly joins the clauses without creating new errors.
A semicolon is appropriate to separate the two independent clauses, and the conjunctive adverb 'consequently' must be followed by a comma.
Using a semicolon resolves the comma splice without creating fragments or run-on errors, while maintaining the logical relationship between the two clauses.

Key Concept

Run-on Sentences and Comma Splices
Estimated Time:1m 0s
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Topics

Run-on Sentences and Comma Splices

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