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Video: Splices and Run-Ons. From the Mr. O series Joining Two Complete Sentences: Period, Semicolon, or Comma + FANBOYS.
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Question banks: October 2026 English question bank
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Difficulty: Medium | Target Time: 45 seconds
This SAT grammar question tests your ability to identify and correct sentence boundary errors, specifically comma splices and sentence fragments.
Comma splices and sentence fragments are two of the most common traps in Digital SAT grammar questions. Spotting the subject and main verb in each clause tells you whether a choice creates a real sentence or a broken one.
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Start 1-day free trial →The Core Grammar Rule: Sentence Boundaries
To master SAT Writing and Language questions, you must understand complete sentences. Every complete sentence must have:
- A subject (who or what the sentence is about).
- A main verb (the action or state of being).
A comma splice is a common error where two complete sentences are incorrectly joined by only a comma. To fix it, use a period, semicolon, or a comma followed by a coordinating conjunction (like 'and,' 'but,' or 'so'). This is a key topic in our SAT grammar rules guide.
A sentence fragment is a group of words punctuated as a sentence but lacking a main subject-verb pair. A frequent fragment on the SAT exam begins with an '-ing' verb (a participle) without a clear subject.
For the six fragment types the SAT uses and three ways to fix each, see SAT sentence fragments: how to spot and fix them.
Your strategy: Check if the choice creates two complete sentences (requiring proper separation) or creates an incomplete fragment.
Step-by-Step Strategy for SAT Grammar Questions
Follow this test prep strategy to tackle sentence structure questions efficiently:
- Read the original sentence. Find the subject and main verb before the blank. In the example, "the space shuttle Discovery" is the subject and "blasted off" is the verb. That makes a complete sentence.
- Analyze what follows. The phrase begins with "lasting." An "-ing" word alone cannot act as a main verb, so what follows is not a standalone sentence.
- Eliminate errors. Rule out any choice that creates a comma splice, a run-on sentence, or an incorrectly punctuated fragment. For more on these rules, see our full SAT grammar rules guide.
SAT Practice Question: Sentence Structure
On April 12, 1985, the space shuttle Discovery blasted off into space commencing Mission ______. After six days and twenty-three hours, the mission ended when the shuttle landed at Kennedy Space Center in Florida.
Which choice completes the text so that it conforms to the conventions of Standard English?
A) STS-51-D, it lasted
B) STS-51-D, lasting
C) STS-51-D lasting
D) STS-51-D. Lasting
Try it yourself, then review the answer breakdown below.
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Correct Answer and Explanation
Choice D is correct. It uses a period after "STS-51-D" to end the first complete sentence. The word "Lasting" then begins a descriptive phrase, a stylistic fragment that provides detail about the mission's duration. The SAT accepts this construction when the fragment is clearly connected for descriptive effect, avoiding a comma splice. For more on this rule, see our full SAT grammar rules guide.
Why the Other Answers Are Incorrect
Choice A: Creates a comma splice error. "It lasted" is a complete sentence (subject: "it," verb: "lasted"). You cannot join two independent clauses with only a comma.
Choice B: Incorrect comma placement. The comma unnecessarily separates the modifying phrase "lasting after six days..." from the noun "Mission STS-51-D" it describes.
Choice C: Creates a run-on sentence. It fuses the mission name and the modifying phrase without any punctuation, harming readability and grammar. For more on this rule, see our full SAT grammar rules guide.
How to Avoid Common SAT Traps
The Global Trap: Relying on what "sounds right" in casual conversation. The SAT English section tests formal, rule-based writing. Always perform the subject-verb check. For a focused review of punctuation rules, see our full SAT grammar rules guide.
The Specific Trap: Mistaking "lasting" for a main verb. Without a helper verb like "was," "-ing" words create fragments.
Key SAT Grammar Rule to Remember: "If it has a subject and a main verb, it is a sentence. Two sentences need more than a comma. No subject-verb pair means it is a fragment."
Why This Question Matters for Your SAT Score
Sentence boundary questions appear regularly on the Digital SAT. According to College Board's official test specifications, the Writing and Language section tests your command of Standard English conventions, including punctuation and sentence structure. Mastering comma splices and fragments directly improves your score on these predictable items. The Test Advantage recommends practicing at least five sentence boundary questions per study session to build automatic recognition of these error types.
How to Practice for Test Day
Use the Bluebook app to take official Digital SAT practice tests. After each test, review every grammar question you missed. Identify whether the error was a comma splice, a fragment, or a run-on. Keep a running list of the patterns you see. For example, if you notice you often miss comma splices with the word "it," drill those specific examples. The Test Advantage's practice platform includes Targeted Practice for each grammar rule, helping you focus on your weakest areas before test day.
Common Mistakes Students Make on Comma Splice Questions
Many students rush through sentence boundary questions because they think they already know the rules. The most common mistake is treating every comma as a potential error. On the SAT, commas are correct in many contexts, including separating items in a list, setting off introductory clauses, and joining two complete sentences with a coordinating conjunction. The error only occurs when a comma alone connects two independent clauses. Another frequent mistake is confusing a participial phrase (like "lasting...") with a main verb. If you see an "-ing" word, check whether it has a helper verb like "was" or "were." Without that helper, the phrase cannot stand as a complete sentence. The Test Advantage's tutors report that students who slow down to identify the subject and verb before looking at the answer choices improve their accuracy on these questions by an average of 20 percent.
How to Apply This Rule on Test Day
When you see a sentence boundary question on the Digital SAT, follow this quick checklist. First, read the entire sentence, not just the part around the blank. Second, identify the subject and main verb in each clause. Third, count the number of complete sentences. If you have two complete sentences, you need a period, a semicolon, or a comma plus a coordinating conjunction. If you have one complete sentence and a fragment, you need to connect them correctly. The Bluebook app's practice tests include several questions that test this exact pattern. By drilling these questions, you train your brain to spot comma splices and fragments automatically. The Test Advantage's practice platform simulates the Bluebook interface, so you get comfortable with the digital format before test day.
Master the Digital SAT with The Test Advantage
Stop guessing and start mastering the logical rules of the digital SAT exam. The Test Advantage offers thousands of premium, exam-accurate practice questions designed to teach you the frameworks, help you avoid traps, and boost your confidence. For a focused review of punctuation rules, check out our full SAT grammar rules guide.
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References and Further Reading
- Official SAT Suite - What Is on the SATSupports: According to College Board's official test specifications, the Writing and Language section tests your command of Standard English conventions, including punctuation and sentence structure.- Official Test Publisher: Directly from the official test publisher, verifying that the Writing and Language section tests Standard English conventions including punctuation and sentence structure.
Frequently Asked Questions
What is a comma splice on the SAT?
A comma splice is an error where two complete sentences are incorrectly joined by only a comma. Fix it with a period, semicolon, or comma plus a coordinating conjunction.
How to fix a sentence fragment on the SAT?
A sentence fragment lacks a main subject-verb pair. Add a subject and verb, or connect it to a complete sentence with proper punctuation.
What is the correct answer to the SAT practice question about the space shuttle Discovery?
Choice D is correct: 'STS-51-D. Lasting' uses a period to end the first sentence, and 'Lasting' begins a descriptive fragment, avoiding a comma splice.
Why is 'lasting' not a main verb on the SAT?
An '-ing' word like 'lasting' cannot act as a main verb without a helper verb like 'was.' It creates a fragment.