Question 146·Medium·Boundaries
Renowned for her groundbreaking research in astrophysics, Sara Chen made headlines when her team captured the first image of a black _____ a feat once deemed impossible.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundary questions, determine whether the text on each side of the blank is an independent clause by checking for a subject and main verb. If the second part is only a descriptive phrase (such as an appositive) rather than a full sentence, set it off with a comma instead of using a period or semicolon.
Hints
Check if the part after the blank is a full sentence
Read only the words after the blank: "a feat once deemed impossible." Ask yourself: does this have a subject and a main verb so that it could stand alone as a sentence?
Match punctuation to clause type
Remember that semicolons and periods go between two complete sentences. Commas often separate extra descriptive phrases from the main clause. Decide which you have here.
Think about how the last phrase relates to what comes before
Is "a feat once deemed impossible" giving new, separate information, or is it describing/commenting on the achievement of capturing the first image of a black hole? How is that kind of description usually punctuated?
Step-by-step Explanation
Understand the sentence structure
Read the full sentence:
"Renowned for her groundbreaking research in astrophysics, Sara Chen made headlines when her team captured the first image of a black _____ a feat once deemed impossible."
The main clause is complete up through "...captured the first image of a black hole." The words after the blank, "a feat once deemed impossible," add extra information about that achievement.
Check whether the words after the blank are an independent clause
Look at what comes after the blank: "a feat once deemed impossible." This does not include a main verb, so it cannot stand alone as a complete sentence.
Instead, it renames/describes the entire idea of capturing the image, which makes it an appositive phrase.
Eliminate punctuation that requires two complete sentences
A semicolon or a period can separate two independent clauses (two complete sentences).
Because "a feat once deemed impossible" is not a complete sentence, we cannot correctly use a semicolon or a period before it.
Use punctuation that sets off an appositive phrase
An appositive phrase that adds nonessential information is typically set off with a comma:
"...captured the first image of a black hole, a feat once deemed impossible."
Therefore, the correct choice is "hole,".