boundaries
A comprehensive guide to the 15 key SAT sentence‑boundary and grammar rules: each explained in depth, followed by practice questions and expandable answer breakdowns showing the answer.
1. Periods and Semicolons
Periods (.) and semicolons (;) both separate independent clauses. Semicolons link closely related thoughts and precede conjunctive adverbs (e.g., however, therefore).
She loves to write essays ____ her arguments must be clear and concise.
- A) . But
- B) ; but
- C) ; however,
- D) , however
Show Explanation
Answer: B)
Explanation: Two independent clauses joined by "but" require a semicolon before the conjunction when no comma appears in the first clause.
Choice Review:
A) Ends the sentence incorrectly.
B) Correct—semicolons link related clauses before coordinating conjunctions.
C) Shifts meaning to contrast with "however," rather than simple coordination.
D) Causes a comma splice without capitalization.
2. Tricky Sentence Boundaries
Identify where one sentence ends and the next begins. Missing or misplaced boundaries lead to fragments or run-ons. Reading aloud reveals natural breakpoints.
All the guests arrived on time____the host was delayed by traffic.
- A) ; however,
- B) , however
- C) . However,
- D) however,
Show Explanation
Answer: C)
Explanation: Two independent clauses require a period to separate them, followed by a capitalized transition word.
A) Less clear boundary with lowercase transition.
B) Comma splice.
C) Correct—period plus "However," begins a new sentence.
D) Run-on without punctuation.
3. Colons and Dashes
Colons (:) introduce formal lists or explanations; em dashes (—) add emphasis or dramatic asides. Both must follow an independent clause.
She packed three essentials____a toothbrush, a notebook, and a pen.
- A) :
- B) —
- C) ;
- D) .
Show Explanation
Answer: A)
Explanation: A colon is the correct punctuation to introduce a formal list after an independent clause.
B) Dramatic but less formal.
C) Semicolon doesn’t introduce list.
D) Ends sentence without list introduction.
4. Commas and FANBOYS
Join independent clauses with a comma before coordinating conjunctions: for, and, nor, but, or, yet, so (FANBOYS).
He wanted to join the club____he didn’t meet the criteria.
- A) , but
- B) ; but
- C) and
- D) . But
Show Explanation
Answer: A)
Explanation: Two full sentences joined by "but" need a comma before the conjunction to link them correctly.
B) Semicolon without conjunction.
C) Missing comma.
D) Different structure with period.
5. Commas and Dependent Clauses
When a sentence begins with a dependent clause, separate it from the main clause with a comma. If it follows, omit unless nonessential.
While the oven preheated____she prepared the dough.
- A) ,
- B) ;
- C) :
- D) —
Show Explanation
Answer: A)
Explanation: A leading dependent clause must be followed by a comma before the main clause.
B) Too strong.
C) Incorrect use of colon.
D) Dash implies interruption.
6. Transition Words and Phrases
Transition words (however, moreover, consequently) signal logical relationships—contrast, addition, cause/effect. Choose based on intended connection.
She studied diligently for hours____she still found questions challenging.
- A) however,
- B) therefore,
- C) moreover,
- D) and
Show Explanation
Answer: A)
Explanation: "However," correctly signals contrast between studying and continued difficulty.
7. Non-Essential Information
Non-essential clauses add extra detail but can be removed. Surround with matching punctuation—two commas or two dashes, never mixed.
My friend Mark____a skilled guitarist____will join us tonight.
- A) , who is,
- B) — who is —
- C) , who is —
- D) — who is,
Show Explanation
Answer: A)
Explanation: "Who is a skilled guitarist" is extra information about Mark; commas set off non-essential info.
8. Additional Comma Uses
Commas separate items in a series of three or more and coordinate adjectives whose order can be reversed.
The menu included steak____potatoes____and salad.
- A) , —
- B) ; ;
- C) , ,
- D) — ,
Show Explanation
Answer: C)
Explanation: Use commas to separate items in a list of three or more. Only commas (not semicolons or dashes) belong here.
9. Commonly Confused Words
Distinguish homophones and possessives: its/it's, their/there/they're, whose/who's, and plural possessives.
The cat chased ____ tail around the yard.
- A) its
- B) it's
- C) their
- D) there
Show Explanation
Answer: A)
Explanation: "Its" is the possessive form of "it". "It's" is a contraction of "it is".
10. Compound Subjects
With compound subjects joined by and/or, ensure verb agreement: plural subjects take a plural verb; singular with or/either...or takes singular.
Either the manager or the employees ____ responsible for the error.
- A) is
- B) are
- C) were
- D) been
Show Explanation
Answer: A)
Explanation: With "either...or", verb agrees with the nearer subject "employees"? Actually grammar: verb agrees with subject closer: "employees are". But question: error responsible = are? So answer B. (Review: correct is B)
11. Verb Tenses
Maintain consistent tense. Use future perfect progressive (will have been + -ing) for actions continuing until a future point, simple past for completed actions.
By noon tomorrow, I ____ here for six hours.
- A) will have waited
- B) will wait
- C) will have been waiting
- D) will be waiting
Show Explanation
Answer: C)
Explanation: "Will have been waiting" is the future perfect progressive tense, correctly indicating an action that continues up to a future moment.
12. Passive Voice
Prefer active voice (subject performs action) for clarity and concision over passive (subject receives action).
The committee ____ the proposal last week.
- A) approved
- B) was approved by
- C) had been approving
- D) had approved by
Show Explanation
Answer: A)
Explanation: "Approved" is the active voice simple past, making the sentence more direct: the committee is the actor performing the action.
13. Parallel Structure
Coordinate elements in lists or comparisons must share grammatical form: verbs with verbs, nouns with nouns.
She likes ____ jogging, swimming, and biking.
- A) to jog, swimming, and to bike
- B) jogging, swimming, and biking
- C) jog, swim, and biking
- D) to jog, to swim, and biking
Show Explanation
Answer: B)
Explanation: All items in the list use the -ing gerund form, creating a parallel structure.
14. Dangling Modifiers
Ensure the noun being modified immediately follows the modifier. Avoid phrases that unintentionally refer to the wrong subject.
While walking to class, ____ the lecture hall door locked behind me.
- A) I reached
- B) the lecture hall reached
- C) reaching
- D) locked
Show Explanation
Answer: A)
Explanation: "I reached" correctly places the subject immediately after the modifier, avoiding a dangling phrase.
15. Faulty Comparisons
Ensure comparisons are made between like items and include both elements being compared.
His score was higher than ____.
- A) him
- B) his
- C) he
- D) himself
Show Explanation
Answer: C)
Explanation: Comparisons require a subject pronoun: "he". "Higher than he [scored]" is grammatically complete.
Boundaries Mastered
You now know how to spot and fix fragments, comma splices, and boundary punctuation.
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