Question 192·Hard·Boundaries
Charged with shielding coastal ecosystems, mangrove roots slow erosion, filter pollutants, and provide nurseries for juvenile fish. Over millennia, what began as a simple adaptation to rising tides has become something far more ______ multitiered defense system that benefits both land and sea.
Which choice completes the text so that it conforms to the conventions of Standard English?
For SAT punctuation/boundary questions, first split the sentence around the blank and test whether each side is an independent clause (full sentence) or a phrase. Then recall what each punctuation mark legally connects: semicolons and periods separate full sentences, commas cannot join two complete sentences by themselves, and colons follow a complete sentence to introduce explanations, lists, or examples. Eliminate any choice that creates a fragment or comma splice, and choose the option whose punctuation matches the actual clause structure and meaning of the sentence.
Hints
Check completeness before the blank
Read from the beginning up to the blank. Does that part already express a complete thought with a subject and verb?
Check completeness after the blank
Read only “multitiered defense system that benefits both land and sea.” Can this stand on its own as a full sentence, or is it just a phrase that describes/renames something?
Think about what the second part is doing
Is the phrase after the blank introducing a new idea, or is it explaining what the “something far more” actually is? Consider what punctuation is commonly used to introduce an explanation or definition after a complete sentence.
Test each punctuation mark’s job
Remember: semicolons and periods generally come before full sentences; commas cannot join two full sentences by themselves. Which choice fits the actual structure you identified?
Step-by-step Explanation
Identify the structure before the blank
Read up to the blank: “Over millennia, what began as a simple adaptation to rising tides has become something far more sophisticated …”
This part has a subject and verb and expresses a complete thought, so it can stand alone as an independent clause (a full sentence).
Identify the structure after the blank
Now read what comes after the blank: “multitiered defense system that benefits both land and sea.”
This is not a complete sentence: it has no finite verb like is or has become. Instead, it’s a noun phrase that renames or explains what the “something far more sophisticated” is.
Decide what kind of punctuation is possible
Because the first part is a full sentence and the part after the blank is a phrase that explains or renames something in that sentence, the punctuation should:
- Not create two separate sentences (because the second part is a fragment on its own).
- Not use a semicolon, which must join two independent clauses.
- Not use just a comma with a new subject and verb, which would create a comma splice.
We need punctuation that can follow a complete sentence and introduce an explanation or restatement.
Match the correct punctuation to the answer choices
Check each choice:
- “sophisticated; a” would use a semicolon, which is incorrect because the words after it are not a full sentence.
- “sophisticated, it became a” creates a comma splice and awkwardly shifts the sentence structure.
- “sophisticated. A” makes the second part a sentence fragment.
- “sophisticated: a” uses a colon after a complete sentence to introduce a phrase that explains what that “something far more sophisticated” is.
Therefore, the correct answer is D) sophisticated: a.