Question 249·Hard·Boundaries
During the mid-twentieth century, the artist Bridget Riley pioneered Op Art _____ a movement characterized by optical illusions created through precise geometric patterns—but her earliest works reveal a strong influence of Impressionism.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation and boundary questions, first strip the sentence down to its core to see which parts are essential and which are extra. Identify any descriptive or nonessential phrases (like appositives) and check how they are opened and closed—commas must pair with commas, and dashes must pair with dashes. Then match each answer choice to the grammatical role needed (joining full sentences, setting off extra information, etc.) and quickly eliminate options that either break clause rules (like misusing semicolons) or create inconsistent punctuation around the same phrase.
Hints
Identify the extra information
Focus on the words “a movement characterized by optical illusions created through precise geometric patterns.” What are they doing in the sentence? What do they describe?
Think about how extra information is set off
When a sentence includes a descriptive phrase that renames or further explains a noun, writers often set it off with commas or dashes. Look at the punctuation after the phrase “geometric patterns.”
Look for matching punctuation
You already have a dash before the word “but.” If that dash is closing off the descriptive phrase, what punctuation should be used after “Op Art” to open that phrase in a parallel way?
Eliminate mismatched options
Eliminate any answer choices that would give you a comma, semicolon, or colon on one side of the descriptive phrase and a dash on the other side.
Step-by-step Explanation
Understand the sentence structure
Read the whole sentence and identify its core:
“During the mid-twentieth century, the artist Bridget Riley pioneered Op Art … but her earliest works reveal a strong influence of Impressionism.”
Between “Op Art” and “but her earliest works,” there is an added descriptive phrase: “a movement characterized by optical illusions created through precise geometric patterns.” This is extra, nonessential information that describes what Op Art is.
Recognize the descriptive phrase (appositive)
The phrase “a movement characterized by optical illusions created through precise geometric patterns” renames and explains “Op Art.”
That kind of renaming phrase is called an appositive and is usually set off from the rest of the sentence with matching punctuation—either commas or a pair of dashes.
Notice the existing dash later in the sentence
After the descriptive phrase, the sentence has a dash before “but”: “patterns—but her earliest works…”
That dash is already closing off the descriptive phrase. To keep the punctuation consistent and correct, the phrase must be opened with the same kind of mark that closes it. So we need punctuation after “Op Art” that matches the dash after “patterns.”
Test each answer choice for parallel punctuation
Only one option uses the same punctuation mark (an em dash) after “Op Art” that we see after “patterns,” creating a matching pair of dashes around the descriptive phrase:
“During the mid-twentieth century, the artist Bridget Riley pioneered **Op Art—a movement characterized by optical illusions created through precise geometric patterns—**but her earliest works reveal a strong influence of Impressionism.”
So the correct answer is Op Art—.