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Sentence boundaries practice

SAT, PSAT and ACT Standard English Conventions · 99 questions in the bank

Boundaries questions ask one thing: is the punctuation between these two pieces of the sentence legal? They are the single most tested item in Standard English Conventions, and they follow a rule you can apply in about four seconds.

Because it is a rule rather than a judgment, this is usually the fastest content area to improve in the whole Reading and Writing section.

How to answer these

  1. Cover each side of the punctuation mark. Ask whether each half could stand alone as a sentence.
  2. If both halves are complete sentences, a comma alone is illegal. That is a comma splice. Legal joins are a period, a semicolon, a colon, or a comma plus a coordinating conjunction (and, but, or, so, for, nor, yet).
  3. If only one half is complete, a semicolon is illegal, because a semicolon needs a full clause on both sides.
  4. Look at what actually differs between the options. Usually it is one mark in one position. Identify that position and ask which rule governs it.

What the wrong answers look like

Practice questions

Four real questions from the CruxStudy bank, with the keyed answer marked and the explanation behind a click so you can try them first.

Example 1Easier
A high school senior started a weekly newsletter about local shows from a corner of the study hall. The newsletter's first issue went out to fourteen ______ most recent issue reached more than nine thousand people.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. subscribers; its correct
  2. subscribers, its
  3. subscribers its
  4. subscribers, therefore its
Show the explanation

Two independent clauses must be separated by a semicolon or an equivalent boundary. A comma alone creates a comma splice, no punctuation creates a run-on, and adding therefore after a comma still splices the clauses.

Example 2Medium
Cuttlefish lack the color-sensing cells found in most vertebrate ______ they can still distinguish hues, perhaps by detecting how different wavelengths focus in their unusual pupils.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. eyes, however,
  2. eyes; however, correct
  3. eyes however,
  4. eyes, however;
Show the explanation

When 'however' links two independent clauses, it needs a semicolon before it and a comma after it. A comma before 'however' produces a comma splice, and a semicolon after it puts the boundary in the wrong place.

Example 3Harder
The app's most-used feature, a price-history chart showing what a sneaker actually sold ______ was added only after resellers complained that listed prices meant nothing.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. for
  2. for;
  3. for, correct
  4. for:
Show the explanation

The description between the commas is a nonrestrictive appositive, and an element opened with a comma must be closed with a comma. A semicolon or colon cannot separate a subject from its verb, and omitting the punctuation leaves the appositive unclosed.

Example 4Medium
Sojourner ______ spent eighty-three days photographing rocks and analyzing soil on the Martian surface.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. , the first rover to operate on another planet
  2. the first rover to operate on another planet,
  3. , the first rover to operate on another planet;
  4. , the first rover to operate on another planet, correct
Show the explanation

A nonessential appositive must be enclosed by a matching pair of commas. The other choices open without closing, close without opening, or wrongly end the appositive with a semicolon.

Drill all 99 of them

Open the drill inside CruxStudy and it serves sentence boundaries questions one at a time, with an explanation after every answer and your accuracy tracked. Free, no account.

Start a drill See the lesson

Common questions

What is a comma splice?

Two complete sentences joined by a comma alone. Fix it with a period, a semicolon, a colon, or a comma plus a coordinating conjunction such as and, but or so.

When do I use a semicolon on the SAT?

Only between two complete sentences that are closely related. If either side could not stand alone, a semicolon is wrong.

Why do I keep getting boundaries questions wrong?

Almost always because you are reading for sound instead of covering each half and asking whether it is a complete sentence. The rule takes four seconds and does not care how the sentence feels.

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