Question 222·Hard·Boundaries
Researchers recently discovered that _____ has begun colonizing Mediterranean lagoons.
Which choice completes the text so that it conforms to the conventions of Standard English?
For punctuation and boundary questions with a descriptive phrase in the middle of a sentence, first decide whether that phrase is essential or extra. Temporarily remove it to see if the sentence still makes sense; if it does, it is nonessential and must be set off with a pair of commas or a pair of dashes. Then quickly scan the options: eliminate any that (1) use mismatched marks (dash + comma), (2) only punctuate one side of the phrase, or (3) leave the phrase unpunctuated so it runs into the main clause.
Hints
Identify the kind of phrase in the blank
Notice that the words in the answer choices rename or describe "the black goby." Think about how English usually punctuates a descriptive phrase that renames a noun.
Test the sentence without the descriptive phrase
Read the sentence as if the descriptive phrase were removed. If the sentence still makes sense, that phrase is extra information and usually needs to be set off with punctuation on both sides.
Look for matching punctuation marks
For extra information in the middle of a sentence, you normally need a matching pair of commas or a matching pair of dashes. Check which option correctly places punctuation both before and after the descriptive phrase.
Step-by-step Explanation
Understand what the blank is doing
Read the full sentence with the idea of a description in mind:
"Researchers recently discovered that the _____ has begun colonizing Mediterranean lagoons."
The words that go in the blank describe or rename "the black goby" (telling us what kind of creature it is). This kind of description is called an appositive (a noun or noun phrase that renames another noun).
Decide if the description is essential or extra
Ask: Do we need "a fish native to the eastern Atlantic" to know which black goby the sentence is talking about?
No—the sentence still makes sense without it:
"Researchers recently discovered that the black goby has begun colonizing Mediterranean lagoons."
Because the description is extra, nonessential information, it should be set off with a pair of matching punctuation marks (commas or dashes) before and after the phrase.
Check for correct punctuation on both sides of the phrase
We need punctuation that:
- Separates the description from "the black goby" on the left, and
- Separates the description from "has begun colonizing Mediterranean lagoons" on the right.
So the correct choice must put matching punctuation marks around "a fish native to the eastern Atlantic" and leave the rest of the sentence as a smooth, complete clause.
Choose the option that correctly sets off the appositive
Test each option in the sentence:
- A) "the black goby—a fish native to the eastern Atlantic, has begun…" mixes a dash on the left with a comma on the right (they do not match), which is incorrect.
- B) "the black goby a fish native to the eastern Atlantic, has begun…" is missing the comma before the description, so the appositive is not properly set off.
- C) "the black goby a fish native to the eastern Atlantic has begun…" has no commas or dashes, so the descriptive phrase runs into the sentence and causes a boundary error.
- D) "the black goby, a fish native to the eastern Atlantic, has begun…" correctly uses a comma before and after the nonessential appositive phrase.
Therefore, the correct answer is D) "the black goby, a fish native to the eastern Atlantic,".