Question 145·Easy·Boundaries
Marine biologists continue to be fascinated by octopuses. These cephalopods possess three hearts and blue blood, but perhaps their most intriguing trait is their brainpower. Octopuses, known for their remarkable ___ can solve puzzles and even escape from seemingly inescapable enclosures.
Which choice completes the text so that it conforms to the conventions of Standard English?
For boundaries questions, first find the core sentence by temporarily removing interrupting descriptive phrases. If the removed phrase is nonessential (the sentence remains complete without it), it should usually be enclosed by commas. Avoid semicolons/colons unless there is a complete independent clause before them, and use dashes only when their placement is consistent (often as a pair).
Hints
Find the main sentence
Mentally skip the interruption "known for their remarkable ___" and check whether the remaining sentence has a subject and a verb.
Decide whether the interruption is essential
Do you need the words "known for their remarkable intelligence" for the sentence to be grammatically complete, or are they just extra description?
Recall how nonessential information is punctuated
When extra information appears in the middle of a sentence, what punctuation mark is typically used on both sides of it?
Eliminate punctuation that needs a full clause before it
Would a semicolon or colon make sense here? Check whether the words before that punctuation would form a complete sentence.
Step-by-step Explanation
Identify the core sentence
Remove the descriptive interruption to see the main structure:
"Octopuses … can solve puzzles and even escape from seemingly inescapable enclosures."
This is a complete sentence with subject ("Octopuses") and verb ("can solve"), so the removed words are extra description.
Classify the descriptive phrase
The words "known for their remarkable intelligence" add extra information about octopuses but are not required for the sentence to be complete.
That makes the phrase a nonessential modifier, which is typically set off with punctuation on both sides.
Choose punctuation that fits nonessential information
Nonessential modifiers in the middle of a sentence are most commonly set off with commas.
Semicolons and colons generally require a complete clause before them, and an em dash would normally be paired with another dash (or at least match the punctuation used to open the interruption).
Apply the rule to the sentence
The sentence already opens the nonessential phrase with a comma: "Octopuses, known for their remarkable …"
So the blank should supply the word and the comma that closes the interruption:
"Octopuses, known for their remarkable intelligence, can solve puzzles …"
Therefore, the correct choice is intelligence,.