Examkin

Dashes

30 questions

All types30Multiple choice15Fill in the blank15
Question 1Question →

The brainless slime mold *Physarum polycephalum* exhibits a remarkable form of primitive intelligence. When placed in a maze with oat flakes at two separate exits, the organism—which is essentially a single, giant cell containing millions of nuclei, soon reorganizes its tubular network to connect the food sources via the shortest route. By pruning inefficient paths and strengthening successful ones, the mold creates a highly optimized network that closely mirrors human-designed transit systems.

Which choice best maintains grammatical consistency and punctuation standards in the passage?

Show answer & explanation

Answer: nuclei—soon reorganizes

Answer

The correct option is the one that closes the parenthetical phrase with an em dash and keeps the active finite verb 'reorganizes'.
The non-essential clause 'which is essentially a single, giant cell containing millions of nuclei' interrupts the main clause and is introduced by an em dash after the subject 'organism'. To maintain punctuation consistency, this non-essential clause must be closed by a matching em dash after the word 'nuclei'. Additionally, the main clause requires the finite verb 'reorganizes' to agree with the subject 'organism'.

Step-by-Step Solution

1
Identify the parenthetical, non-essential clause in the sentence.
The clause 'which is essentially a single, giant cell containing millions of nuclei' is parenthetical and non-essential to the main sentence structure.
Recognizing non-essential clauses helps determine the appropriate punctuation boundaries.
2
Check the punctuation opening the parenthetical clause.
The clause is opened by an em dash after the word 'organism'.
Parenthetical elements must be enclosed by matching punctuation marks: either two commas, two parentheses, or two em dashes.
3
Select the choice that closes the parenthetical clause with a matching em dash.
The option containing 'nuclei—' successfully matches the opening em dash.
Punctuation consistency requires an em dash to close a parenthetical insert that began with an em dash.
4
Verify that the main clause contains a complete subject and verb combination.
Using the finite verb 'reorganizes' allows the subject 'the organism' to have a predicate, whereas the participle 'reorganizing' creates a fragment.
The sentence must have a complete independent clause once the parenthetical information is removed.

Key Concept

Dash consistency for parenthetical elements
Question 2Question →

Read the passage below. The first sentence contains a nonessential parenthetical phrase that is introduced by a dash. What punctuation mark should be placed in the blank to maintain punctuation consistency and correctly set off this phrase?

Fill in the blanks below

In 1974, a team of glaciologists embarked on a pioneering expedition to retrieve ice cores from the Quelccaya Ice Cap—the largest ice mass in the tropicshoping to reconstruct a detailed history of the region's climate. The ancient ice contains dust particles, volcanic ash, and chemical signatures that reveal past weather patterns. By analyzing these layers, the scientists successfully created a year-by-year climate record spanning over fifteen centuries.
Show answer & explanation

Answer

A dash (—)
The sentence contains a nonessential parenthetical phrase, 'the largest ice mass in the tropics,' which describes the 'Quelccaya Ice Cap.' Under standard conventions, nonessential phrases must be enclosed by matching punctuation marks (either a pair of commas, a pair of parentheses, or a pair of dashes). Because the phrase begins with a dash after 'Quelccaya Ice Cap,' it must end with a matching dash before 'hoping' to ensure consistency and grammatical correctness.

Step-by-Step Solution

1
Identify the parenthetical (nonessential) phrase in the sentence.
The phrase 'the largest ice mass in the tropics' provides extra, nonessential information about the 'Quelccaya Ice Cap'.
Recognizing the structure of the sentence helps determine which punctuation rules apply.
2
Observe the punctuation mark that introduces the parenthetical phrase.
The parenthetical phrase is introduced by an em dash (—).
Parenthetical elements must be set off by matching punctuation marks.
3
Determine the correct punctuation mark to close the parenthetical phrase.
To match the opening dash and maintain punctuation consistency, the phrase must be closed with a dash.
Mixing a dash with a comma or parenthesis is incorrect under standard ACT punctuation conventions.

Key Concept

Punctuation consistency with parenthetical elements (dashes)
Question 3Question →

The passage below contains a sentence with a missing punctuation mark. Read the passage and determine the correct punctuation mark needed to complete the sentence. Which punctuation mark must fill the blank to ensure proper punctuation consistency?

Fill in the blanks below

The majestic monarch butterfly—known for its vibrant orange and black wingsembarks on a spectacular multi-generational migration across North America.
Show answer & explanation

Answer

A dash (—)
The correct punctuation mark is a dash. The sentence contains a nonessential phrase, 'known for its vibrant orange and black wings', which is introduced by a dash. To maintain grammatical consistency, a matching dash must be used to close the parenthetical phrase before the main verb 'embarks'.

Step-by-Step Solution

1
Identify the structure of the sentence and locate the parenthetical (nonessential) modifier.
The phrase 'known for its vibrant orange and black wings' provides extra description of the butterfly and is nonessential to the main clause.
Identifying the nonessential modifier helps determine which punctuation marks are required to set it off from the rest of the sentence.
2
Check the punctuation mark that introduces the nonessential modifier.
The modifier begins with an em dash (—).
To maintain grammatical consistency, the punctuation mark used to open a nonessential phrase must match the punctuation mark used to close it.
3
Select the correct punctuation mark to close the nonessential modifier.
A matching em dash (—) must fill the blank.
Using another punctuation mark, such as a comma, would create an ungrammatical mismatch.

Key Concept

Dash consistency in setting off nonessential clauses
Question 4Question →

The following passage is an excerpt from a biography of Filippo Brunelleschi.

Filippo Brunelleschi’s dome for the Florence Cathedral remains a marvel of the Renaissance. The massive brick structure—a masterpiece of Renaissance engineering, puzzled contemporary builders who deemed its construction impossible without temporary wooden scaffolding. Brunelleschi resolved this challenge by inventing an entirely new hoisting machine and utilizing a herringbone brick-laying pattern.

Which of the following choices best completes the sentence, ensuring correct punctuation and sentence structure?

Show answer & explanation

Answer: engineering—puzzled

Answer

The correct option is the one that reads 'engineering—puzzled', as it uses a matching em dash to close the nonessential parenthetical phrase.
The correct choice is 'engineering—puzzled'. The phrase 'a masterpiece of Renaissance engineering' is a nonessential appositive that interrupts the main flow of the sentence to describe the 'massive brick structure'. Because this nonessential element begins with an em dash, it must also end with an em dash to maintain punctuation consistency. This allows the main subject, 'structure', to connect properly with its verb, 'puzzled'.

Step-by-Step Solution

1
Identify the role of the underlined phrase within the sentence.
The phrase 'a masterpiece of Renaissance engineering' is a nonessential parenthetical appositive that describes the 'massive brick structure'.
Knowing the function of the phrase helps determine how it should be punctuated.
2
Locate the punctuation mark that introduces the parenthetical phrase.
The phrase begins with an em dash ('structure—a masterpiece...').
Nonessential phrases must be enclosed by matching punctuation marks (commas, parentheses, or dashes).
3
Determine the correct punctuation mark needed to close the parenthetical phrase.
Since the phrase began with a dash, it must be closed with a dash ('engineering—puzzled') to maintain consistency.
A mismatched closing punctuation mark (like a comma) is incorrect.
4
Verify that the main clause remains structurally complete.
The main clause 'The massive brick structure puzzled contemporary builders...' has a subject ('structure') and a verb ('puzzled') and is grammatically correct.
Ensuring the sentence does not become a fragment or run-on confirms the correct choice.

Key Concept

Matching Parenthetical Punctuation (Dashes)
Estimated Time:1m 0s
Question 5Question →

In the passage below, a punctuation mark is missing. Fill in the blank with the correct punctuation mark (such as a comma, semicolon, colon, or dash) that should be placed in the sentence to ensure it is grammatically correct and internally consistent.

Fill in the blanks below

Although Michael Ventris is often credited with deciphering Linear B, the historic breakthrough relied heavily on the meticulous preparation of classicist Alice Kober. For years, Kober cataloged the symbols on hand-cut index cards—which she stored in cardboard boxes due to wartime paper shortages to identify patterns in the script's inflected grammatical endings. Her rigorous analysis ultimately proved that Linear B represented an inflected Indo-European language, setting the stage for its final decipherment.
Show answer & explanation

Answer

An em dash (—) is required to close the nonessential parenthetical clause that was introduced by the preceding em dash.
A dash is required to maintain consistency with the em dash that introduces the nonessential parenthetical clause ('which she stored in cardboard boxes due to wartime paper shortages'). In English grammar, parenthetical elements must be set off by matching punctuation marks: either a pair of commas, a pair of parentheses, or a pair of dashes. Since the clause begins with a dash after 'cards', it must end with a dash before 'to identify'.

Step-by-Step Solution

1
Identify the syntactic structure of the sentence containing the blank.
The phrase 'which she stored in cardboard boxes due to wartime paper shortages' is a nonessential parenthetical clause describing the index cards.
Identifying parenthetical elements is necessary to determine the appropriate punctuation rules.
2
Check the punctuation mark that introduces the nonessential parenthetical clause.
The clause is introduced by an em dash (—) after the word 'cards'.
Standard grammar rules dictate that punctuation setting off a parenthetical element must be consistent at both the beginning and the end.
3
Apply the rule of punctuation consistency to select the closing punctuation mark.
Because the parenthetical clause begins with an em dash, it must also end with an em dash (—).
Mismatching punctuation marks (for example, starting a parenthetical element with a dash and ending it with a comma) is incorrect.

Key Concept

Consistent punctuation for nonessential clauses using dash pairs
Estimated Time:1m 0s
Question 6Question →

The passage below contains a blank indicating a missing punctuation mark. Fill in the blank with the punctuation mark that correctly completes the sentence, maintaining consistency with the punctuation already used to set off the nonessential clause.

Fill in the blanks below

In 1967, astrophysicist Jocelyn Bell Burnell detected a series of repeating radio signals—initially dubbed 'Little Green Men' as a jokethat turned out to be the first discovered pulsar.
Show answer & explanation

Answer

An em dash (—) or double hyphen (--) must be used to close the nonessential parenthetical phrase.
The sentence uses an em dash (—) to open the nonessential parenthetical phrase 'initially dubbed "Little Green Men" as a joke'. Under standard punctuation rules tested on the ACT, nonessential phrases set off by dashes must be closed with a matching dash. Therefore, an em dash (—) or its keyboard representation (--) is required to correctly complete the sentence.

Step-by-Step Solution

1
Identify the parenthetical (nonessential) clause in the sentence.
The phrase 'initially dubbed "Little Green Men" as a joke' provides extra, nonessential information about the radio signals.
Nonessential information must be set off from the rest of the sentence by matching punctuation marks on both sides.
2
Examine the punctuation mark that opens the parenthetical clause.
An em dash (—) precedes 'initially'.
This establishes that dashes are being used as the punctuation style for this parenthetical element.
3
Determine the matching punctuation mark needed to close the parenthetical clause.
Another em dash (—) or double hyphen (--) is required before 'that'.
To maintain punctuation consistency, a dash must be paired with another dash; pairing a dash with a comma, semicolon, or parenthesis is incorrect.

Key Concept

Punctuation consistency with parenthetical elements requires using matching marks (dash with dash, comma with comma, parenthesis with parenthesis) to set off nonessential information.
Estimated Time:45s
Question 7Question →

The following passage is an excerpt from an essay on archaeological discoveries.

For decades, scholars believed that the clay tablets discovered at the ancient palace of Knossos were written in an indigenous, non-Greek tongue. However, in 1952, Michael Ventris proved this assumption wrong. Deciphering the Knossos tablets required Ventris to cross-reference thousands of character combinations—a process made significantly more difficult by the damaged state of the clay, and to construct a grid of grammatical relationships. Ultimately, his work revealed that the script, known as Linear B, was an early form of Greek.

Which of the following choices is the best version of the underlined portion of the sentence?

Show answer & explanation

Answer: combinations—a process made significantly more difficult by the damaged state of the clay—and

Answer

The correct option is the one that sets off the parenthetical phrase with matching dashes on both sides, reading: 'combinations—a process made significantly more difficult by the damaged state of the clay—and'
The correct answer correctly uses a pair of dashes to set off the nonessential appositive phrase ('a process made significantly more difficult by the damaged state of the clay'). Nonessential elements must be set off with consistent punctuation at both ends. Since the parenthetical phrase begins with a dash, it must also end with a dash.

Step-by-Step Solution

1
Identify the syntactic role of the underlined phrase.
The phrase starting with 'a process...' is a nonessential appositive that clarifies why the cross-referencing was difficult.
Nonessential elements must be set off from the rest of the sentence using punctuation marks such as commas, parentheses, or dashes.
2
Check for consistency in the punctuation marks wrapping the nonessential phrase.
The phrase starts with an em-dash after the word 'combinations'. Therefore, it must also end with an em-dash before 'and' to maintain consistency.
Mixing a dash at the beginning of a parenthetical phrase with a comma at the end violates the rule of punctuation pair consistency.
3
Verify that other punctuation marks like semicolons are not appropriate here.
Semicolons are incorrect because neither the appositive phrase nor the subsequent parallel infinitive phrase ('and to construct...') is an independent clause.
A semicolon is used to connect two independent clauses; using it to separate phrases creates grammatical fragments.

Key Concept

Punctuation consistency with parenthetical elements and dashes
Question 8Question →

Identify the punctuation mark that should fill the blank to ensure the sentence is grammatically correct and consistent.

Fill in the blanks below

Although the standard theory of planet formation suggests that gas giants form far from their host stars—where temperatures are low enough for volatile compounds to condense the discovery of 'hot Jupiters' orbiting mere fractions of an astronomical unit from their stars has forced astrophysicists to revise their models of planetary migration.
Show answer & explanation

Answer

A dash (—)
The parenthetical clause detailing where gas giants form ('—where temperatures are low enough for volatile compounds to condense') is opened with an em dash. To maintain grammatical consistency, the clause must also be closed with a dash. A dash is the only punctuation mark that correctly completes this pair.

Step-by-Step Solution

1
Analyze the structure of the sentence, focusing on the parenthetical element setting off the description of where gas giants form.
Identify that the parenthetical clause begins with an em dash ('—where temperatures are low enough for volatile compounds to condense').
To set off parenthetical or nonessential information, punctuation marks must be consistent on both sides.
2
Determine the matching punctuation mark needed to close the parenthetical element before the main clause begins.
Since the parenthetical phrase is opened with a dash, it must be closed with a dash to maintain consistency.
Mismatching a dash with a comma or parenthesis is grammatically incorrect in standard English conventions.

Key Concept

Dash pair consistency for nonessential parenthetical elements
Question 9Question →

Maya Angelou wrote seven autobiographies during her lifetime. The first of these books [underlined]—*I Know Why the Caged Bird Sings*, which was published in 1969, became[/underlined] a landmark of American literature.

Which of the following choices best replaces the underlined portion to ensure proper punctuation?

Show answer & explanation

Answer: —*I Know Why the Caged Bird Sings*, which was published in 1969—became

Answer

The version that matches the opening dash with a closing dash before the verb 'became' is correct.
The correct option uses a matching dash after '1969' to pair with the dash that appears before the book title. This creates a consistent pair of dashes setting off the nonessential appositive phrase describing the book.

Step-by-Step Solution

1
Identify the nonessential information in the sentence that is being set off.
The phrase '*I Know Why the Caged Bird Sings*, which was published in 1969' is nonessential appositive information detailing the first book.
Recognizing the boundaries of nonessential information helps determine where the surrounding punctuation must go.
2
Check the punctuation mark that introduces the nonessential phrase.
The phrase is introduced with a dash.
Consistent punctuation is required; a dash at the beginning of a parenthetical insertion must be paired with another dash at the end of the insertion.
3
Select the option that terminates the phrase with a matching dash before resuming the main clause.
The correct option ends the nonessential phrase with a dash right before the verb 'became'.
This ensures the sentence is grammatically correct and consistent in its punctuation.

Key Concept

Dashes are used to set off nonessential (parenthetical) information in a sentence. When doing so, the punctuation marks must be consistent: either a pair of commas or a pair of dashes. A dash at the beginning of a nonessential phrase must be matched by a dash at the end.
Question 10Question →

The sentence below contains a nonessential phrase that begins with a dash. To ensure grammatical correctness and punctuation consistency, which punctuation mark should be placed in the blank to close this nonessential phrase?

Fill in the blanks below

Marine biologists have recently discovered that the Greenland shark—the longest-lived vertebrate animal known to sciencecan live for nearly four centuries.
Show answer & explanation

Answer

A dash (—)
A dash is the correct punctuation mark because it matches the dash used to open the parenthetical phrase 'the longest-lived vertebrate animal known to science'. In standard English grammar, parenthetical elements set off by dashes must be enclosed by a consistent pair of dashes.

Step-by-Step Solution

1
Identify the nonessential phrase in the sentence.
The phrase 'the longest-lived vertebrate animal known to science' is a nonessential appositive that describes the 'Greenland shark'.
Nonessential elements add extra details but can be removed from the sentence without changing its core meaning.
2
Determine the punctuation mark used to open the nonessential phrase.
The nonessential phrase begins with a dash ('—') after 'Greenland shark'.
Nonessential phrases must be set off by matching punctuation marks on both sides.
3
Select the correct closing punctuation mark.
A matching dash must be placed in the blank to close the nonessential phrase.
Mismatching punctuation marks (such as starting with a dash and ending with a comma) is grammatically incorrect.

Key Concept

Dash Pair Consistency
Estimated Time:45s
Question 11Question →

Although often confused with the giant panda, the red panda is in its own unique evolutionary family. The red panda—a small mammal native to the eastern [underlined]Himalayas, is known[/underlined] for its bright reddish-brown fur and acrobatic climbing skills.

Which of the following choices best maintains punctuation consistency in the sentence?

Show answer & explanation

Answer: Himalayas—is known

Answer

The correct option is the phrase that replaces the comma with a dash to match the opening dash, resulting in 'Himalayas—is known'.
The sentence contains a parenthetical, nonessential phrase ('a small mammal native to the eastern Himalayas') that is introduced with a dash. To ensure grammatical correctness and punctuation consistency, the phrase must also be closed with a dash. The correct option successfully provides this matching dash, linking the subject 'red panda' directly and cleanly to its verb 'is known'.

Step-by-Step Solution

1
Identify the parenthetical nonessential phrase in the sentence.
The phrase is 'a small mammal native to the eastern Himalayas'.
Nonessential phrases provide extra information and must be set off from the rest of the sentence by consistent punctuation on both sides.
2
Determine the opening punctuation mark of the parenthetical phrase.
The phrase is introduced with a dash after the word 'panda'.
To maintain punctuation consistency, parenthetical elements must be enclosed by matching punctuation marks: either two commas, two parentheses, or two dashes.
3
Select the option that closes the parenthetical phrase with a matching dash.
Replacing the comma with a dash after 'Himalayas' closes the phrase consistently.
This maintains the matching pair of dashes and avoids punctuation mismatches.

Key Concept

Dashes must be used in consistent pairs when enclosing nonessential or parenthetical information in a sentence.
Estimated Time:45s
Question 12Question →

The following passage contains a sentence with a missing punctuation mark. What punctuation mark should be placed in the blank to complete the sentence with consistent and grammatically correct punctuation?

Fill in the blanks below

Coastal redwoods are among the oldest and most resilient organisms in the world. These massive trees—the tallest living things on Earthcan reach heights of over 350 feet and live for more than two thousand years.
Show answer & explanation

Answer

An em dash (—) or dash
A dash is required to close the nonessential phrase because the phrase was opened with a dash. To maintain punctuation consistency, any parenthetical element set off by dashes must use a dash at both the beginning and the end.

Step-by-Step Solution

1
Identify the nonessential parenthetical phrase in the sentence.
The phrase is 'the tallest living things on Earth', which provides extra descriptive information about 'These massive trees'.
Recognizing the boundary of the nonessential element is necessary to determine what punctuation is needed to set it off from the rest of the sentence.
2
Examine the punctuation mark that opens the nonessential phrase.
An em dash (—) appears right before 'the tallest living things on Earth'.
Punctuation marks that set off parenthetical elements must be consistent on both sides.
3
Determine the punctuation mark needed to close the nonessential phrase.
A matching em dash (—) is required to close the phrase before the main verb 'can reach'.
Mixing a dash with another punctuation mark (like a comma) is incorrect; a dash must be matched with another dash.

Key Concept

Dashes
Estimated Time:45s
Question 13Question →

The following passage is an excerpt from a science article about deep-sea marine biology.

Deep-ocean hydrothermal vents support thriving ecosystems in some of the most hostile environments on Earth. Organisms living near these vents—such as the giant tube worm, which lacks a mouth and digestive tract, rely on symbiotic bacteria for survival. These bacteria convert toxic chemicals from the vents into usable energy.

Which choice is the best replacement for the underlined portion of the sentence?

Show answer & explanation

Answer: tract—rely

Answer

The correct choice is the option that replaces the underlined text with 'tract—rely', using a dash to match the opening dash and properly close the nonessential phrase.
The sentence contains a nonessential parenthetical phrase ('such as the giant tube worm, which lacks a mouth and digestive tract') that is introduced by a dash. To maintain punctuation consistency, the phrase must also close with a dash. The correct choice provides this closing dash, properly separating the parenthetical information from the main verb 'rely'.

Step-by-Step Solution

1
Identify the nonessential parenthetical phrase within the sentence.
The phrase is 'such as the giant tube worm, which lacks a mouth and digestive tract'.
Determining where the parenthetical information begins and ends helps identify the punctuation needed to set it off.
2
Locate the punctuation mark used to introduce the parenthetical phrase.
A dash is used right before the phrase ('vents—such').
Standard punctuation rules require that parenthetical elements be set off by matching punctuation marks: either two commas or two dashes.
3
Evaluate the choices to find the punctuation mark that matches the opening dash.
A closing dash ('tract—rely') is required to maintain consistency and correctly connect the subject to the main verb.
Using a comma, semicolon, or period disrupts the sentence structure and violates punctuation consistency rules.

Key Concept

Punctuation consistency with parenthetical dashes
Question 14Question →

Dorothy Hodgkin, a pioneer in X-ray crystallography, determined the structures of important biochemical substances. Her most famous breakthrough—the structure of penicillin, was resolved in 1945 after years of meticulous analysis.

Which of the following options is the best alternative to the underlined portion of the sentence?

Show answer & explanation

Answer: breakthrough—the structure of penicillin—was

Answer

breakthrough—the structure of penicillin—was
The correct answer properly utilizes matching em dashes to enclose the non-essential appositive phrase 'the structure of penicillin'. In standardized English grammar, non-essential elements must be set off with identical punctuation marks on both sides. Since an em dash is used to open the phrase, a second em dash must close it before the sentence's main verb.

Step-by-Step Solution

1
Identify the non-essential phrase in the sentence that provides additional, parenthetical information.
The phrase 'the structure of penicillin' is a non-essential appositive that clarifies what the 'most famous breakthrough' refers to.
Identifying the non-essential phrase helps determine that it must be set off from the rest of the sentence using consistent punctuation marks at both its start and end.
2
Evaluate the punctuation surrounding the non-essential phrase to ensure consistency.
An em dash is used immediately before the phrase. To maintain punctuation consistency, a matching em dash must be used immediately after the phrase before the main verb.
ACT grammar rules state that parenthetical elements must be enclosed by matching punctuation marks: either two commas, two parentheses, or two em dashes. Mixing an em dash with a comma is incorrect.

Key Concept

Using matching pairs of dashes to set off non-essential parenthetical information.
Estimated Time:45s
Question 15Question →

Read the passage below. Which punctuation mark should be placed in the blank to ensure the sentence is grammatically correct and internally consistent?

Fill in the blanks below

Though he never completed a working prototype, Charles Babbage envisioned a device that would lay the foundation for modern computing. The development of this theoretical machine—the Analytical Engine, a general-purpose computer designed to utilize punched cards for programming anticipated the digital age by nearly a century. Babbage’s collaborator, Ada Lovelace, even wrote the first algorithm intended for the engine, cementing their place in technological history.
Show answer & explanation

Answer

A dash (or em dash) is required to close the nonessential parenthetical phrase that begins with a dash.
A dash is required to close the parenthetical element. Because the parenthetical phrase starts with a dash after 'machine,' it must be closed with a matching dash after 'programming' to maintain consistent punctuation structure.

Step-by-Step Solution

1
Identify the nonessential parenthetical phrase within the sentence.
The phrase is 'the Analytical Engine, a general-purpose computer designed to utilize punched cards for programming'.
Determining where the parenthetical information begins and ends is necessary to apply the correct punctuation rules.
2
Examine the punctuation mark used to open the parenthetical phrase.
An em dash ('—') is placed immediately after 'theoretical machine' to introduce the parenthetical phrase.
Punctuation marks that set off nonessential information must be symmetrical and consistent.
3
Determine the correct punctuation mark for the blank to close the phrase.
Since the phrase began with a dash, it must close with a matching dash after 'programming'.
Mismatching punctuation marks (such as using a comma to close a phrase opened with a dash) is grammatically incorrect on the ACT.

Key Concept

Dash consistency in parenthetical elements
Question 16Question →

Marie Tharp was an American geologist and oceanographic cartographer who, in partnership with Bruce Heezen, created the first scientific map of the entire ocean floor. During the 1950s, much of the ocean floor remained a mystery—a vast, unexplored expanse hidden beneath miles of water—which challenged prevailing geological theories. Tharp's work revealed the presence of the Mid-Atlantic Ridge, a discovery that proved essential to the development of the theory of plate tectonics.

Which of the following choices best punctuates the underlined portion of the sentence?

Show answer & explanation

Answer: NO CHANGE

Answer

mystery—a vast, unexplored expanse hidden beneath miles of water—which
The correct option maintains grammatical consistency by using a matching pair of dashes to enclose the non-essential parenthetical phrase 'a vast, unexplored expanse hidden beneath miles of water.' This allows the relative clause starting with 'which' to correctly connect to the main clause.

Step-by-Step Solution

1
Identify the non-essential parenthetical phrase in the sentence.
The phrase 'a vast, unexplored expanse hidden beneath miles of water' acts as parenthetical information that modifies the noun 'mystery' and can be removed without affecting the core grammatical structure of the sentence.
Recognizing parenthetical elements helps determine the appropriate rules for punctuation alignment.
2
Check the surrounding punctuation for consistency.
Because the parenthetical phrase is introduced by a dash, it must also end with a dash before continuing with the relative clause ('which challenged...').
Non-essential elements must be set off with matching punctuation marks (two commas, two parentheses, or two dashes) to maintain grammatical consistency.

Key Concept

Consistency in setting off non-essential elements with matching punctuation
Question 17Question →

The following passage contains a blank where a punctuation mark is missing. What punctuation mark should be placed in the blank to ensure the sentence is punctuated correctly?

Fill in the blanks below

In the late 1970s, NASA embarked on a grand tour of the outer planets. Launched in 1977, the Voyager 1 spacecraft—the first human-made object to enter interstellar spacecontinues to transmit valuable data back to Earth from billions of miles away. This historic mission has forever changed our understanding of the cosmos.
Show answer & explanation

Answer

A dash (—) must be placed in the blank to close the nonessential parenthetical phrase.
The sentence contains a nonessential parenthetical phrase, 'the first human-made object to enter interstellar space,' which describes the Voyager 1 spacecraft. Because this phrase is introduced by a dash, it must be closed with a matching dash to maintain punctuation consistency. Using any other punctuation mark, such as a comma or a semicolon, would result in an incorrect mixture of punctuation styles.

Step-by-Step Solution

1
Identify the parenthetical (nonessential) phrase in the sentence.
The phrase is 'the first human-made object to enter interstellar space', which describes 'the Voyager 1 spacecraft'.
Recognizing parenthetical elements helps determine how they should be set off from the rest of the sentence.
2
Check the punctuation mark that introduces the parenthetical phrase.
An em dash (—) is used immediately before the phrase.
Nonessential phrases must be enclosed by matching punctuation marks (either a pair of commas, a pair of parentheses, or a pair of dashes).
3
Determine the correct punctuation mark to close the phrase.
A matching dash (—) must be used at the end of the phrase before the main verb 'continues'.
Using a different punctuation mark, such as a comma or semicolon, would violate the rule of punctuation consistency for nonessential elements.

Key Concept

Punctuation consistency with nonessential elements
Estimated Time:1m 0s
Question 18Question →

Read the passage below. Which punctuation mark should be placed in the blank to ensure the sentence is punctuated correctly?

Fill in the blanks below

New Caledonian crows are renowned for their sophisticated tool-making abilities. In the wild, these remarkable birds—often compared to primates in terms of cognitive capacity create hooks from twigs to extract insects from deep crevices.
Show answer & explanation

Answer

A dash (—)
The correct punctuation mark is a dash. The phrase 'often compared to primates in terms of cognitive capacity' is a parenthetical insert. Because the insert begins with a dash after 'birds', it must be closed with a matching dash before the main verb 'create'.

Step-by-Step Solution

1
Identify the parenthetical (nonessential) phrase in the sentence.
The phrase 'often compared to primates in terms of cognitive capacity' is parenthetical and nonessential to the grammatical structure of the main clause.
Nonessential information must be set off from the rest of the sentence using consistent punctuation marks.
2
Analyze the punctuation mark that introduces the parenthetical phrase.
An em dash (—) is used right after the word 'birds' to introduce the phrase.
To maintain punctuation consistency, the punctuation mark closing a parenthetical element must match the one that opened it.
3
Select the matching punctuation mark to close the phrase before the main verb.
A matching em dash (—) must be placed in the blank to correctly set off the phrase.
Mixing a dash with a comma or parenthesis to set off the same nonessential element is grammatically incorrect on the ACT.

Key Concept

Punctuation consistency with dashes setting off nonessential elements
Question 19Question →

The paragraph below contains an underlined portion in brackets.

In 1964, radio astronomers Arno Penzias and Robert Wilson detected a persistent background noise that they could not explain. This mysterious [hum, later identified as the cosmic microwave background radiation, the thermal echo of the Big Bang—was] coming from all directions in the sky. To rule out local interference, they even cleaned the horn antenna of pigeon droppings, but the signal remained.

Which of the following options is the correct punctuation for the underlined portion in brackets?

Show answer & explanation

Answer: hum—later identified as the cosmic microwave background radiation, the thermal echo of the Big Bang—was

Answer

The option that uses consistent dashes ('hum—later identified as the cosmic microwave background radiation, the thermal echo of the Big Bang—was') is correct.
A pair of dashes is used to set off non-essential parenthetical information. In this sentence, the phrase beginning with 'later identified' and ending with 'Big Bang' is non-essential and contains internal commas. To set this phrase off cleanly and consistently, matching dashes must be used at both the beginning and the end of the phrase.

Step-by-Step Solution

1
Identify the parenthetical, non-essential nature of the phrase inside the brackets.
The phrase 'later identified as the cosmic microwave background radiation, the thermal echo of the Big Bang' is non-essential because the main sentence ('This mysterious hum was coming from all directions in the sky') remains grammatically complete without it.
Determining whether the phrase is non-essential helps establish which punctuation rules apply.
2
Check the punctuation marking the boundaries of the non-essential phrase for consistency.
Because the phrase contains internal commas, setting it off with a consistent pair of dashes is the clearest and most grammatical choice. The original text mismatches a comma at the beginning with a dash at the end.
Non-essential phrases must be enclosed by matching punctuation marks (either two commas or two dashes), and mismatching them is incorrect.

Key Concept

Using matching punctuation (such as a pair of dashes) to consistently set off parenthetical or non-essential information within a sentence.
Question 20Question →

Artemisia Gentileschi, a prominent Baroque painter, is celebrated today for her dynamic and dramatic compositions. Her most famous [work—*Judith Slaying Holofernes*, showcases] her mastery of chiaroscuro, a technique that uses strong contrasts between light and dark to create a sense of volume. While many of her contemporaries focused on idealized figures, Gentileschi depicted her subjects with raw, unfiltered emotion.

Which choice represents the correct punctuation for the underlined portion in brackets?

Show answer & explanation

Answer: work—*Judith Slaying Holofernes*—showcases

Answer

The choice that uses a pair of dashes, 'work—*Judith Slaying Holofernes*—showcases', is correct.
The correct option correctly uses a matched pair of dashes to enclose the nonessential appositive '*Judith Slaying Holofernes*'. When a dash is used to introduce a parenthetical element, another dash must be used to close it before the sentence resumes with the verb.

Step-by-Step Solution

1
Identify the parenthetical or nonessential element in the sentence.
The title of the painting, '*Judith Slaying Holofernes*', acts as an appositive explaining which work is being referred to, making it a nonessential element.
Nonessential elements must be set off from the rest of the sentence by consistent punctuation marks on both sides.
2
Evaluate the punctuation surrounding the nonessential element.
The sentence begins the nonessential element with a dash after 'work'. Therefore, it must also end the nonessential element with a dash before the verb 'showcases'.
Punctuation pairs (dashes, commas, or parentheses) must be consistent; you cannot open a nonessential phrase with a dash and close it with a comma.

Key Concept

Consistent use of punctuation pairs to set off nonessential or parenthetical elements in a sentence.
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Dashes Practice Questions — ACT | Examkin