Question 192·Hard·Boundaries
Researchers long assumed that the glass frog’s see-through skin served primarily as _____ recent studies reveal that the translucence may also facilitate thermal regulation by allowing heat to dissipate more effectively.
Which choice completes the text so that it conforms to the conventions of Standard English?
For clause-boundary questions, first test whether the words before and after the blank can each stand alone as complete sentences (subject + verb and a complete thought). If both sides are independent clauses and there is no coordinating conjunction (and, but, or, so, yet, for, nor), eliminate any answer with just a comma or no punctuation, since those create run-ons. Then decide between strong marks (semicolon, colon, or period) based on meaning: use a semicolon when simply linking two related independent clauses, and a colon only when the second part directly explains, defines, or illustrates the first. This quick check prevents most punctuation errors on the SAT.
Hints
Check what comes after the blank
Look closely at the words after the blank: does 'recent studies reveal that the translucence may also facilitate thermal regulation...' form a complete sentence on its own?
Think about the relationship between the two parts
Is the second part simply explaining or listing something from the first part, or is it adding a new, separate idea that contrasts with the earlier assumption?
Match punctuation to clause type
When two complete sentences are joined with no linking word, what kind of punctuation is usually needed between them to avoid a run-on?
Be wary of common errors
A single comma or no punctuation between two complete sentences is usually incorrect. Eliminate any choices that would create that problem here.
Step-by-step Explanation
Identify the two clauses
Break the sentence at the blank:
- First part: 'Researchers long assumed that the glass frog’s see-through skin served primarily as camouflage'
- Second part: 'recent studies reveal that the translucence may also facilitate thermal regulation by allowing heat to dissipate more effectively.'
Each part has its own subject and verb (first: 'Researchers assumed'; second: 'studies reveal'), so both are independent clauses (complete sentences).
Decide the needed punctuation type
When you put two independent clauses together without a joining word like 'and' or 'but', you must separate them with strong punctuation (such as a period, a semicolon, or sometimes a colon).
A comma alone or no punctuation at all would create a run-on sentence and is not acceptable here.
Evaluate whether a colon fits the meaning
A colon is used when the second part explains, defines, or gives an example of the first part (you can often think 'namely' or 'that is').
Here, the second clause adds new, contrasting information: not just camouflage, but also thermal regulation. It does not simply explain or list out the first clause, so a colon is not the best choice.
Choose the correct strong punctuation mark
Because we have two closely related independent clauses without a conjunction, and the second clause is not just an explanation of the first, the best choice is to link them with a semicolon.
So the sentence should read:
'Researchers long assumed that the glass frog’s see-through skin served primarily as camouflage; recent studies reveal that the translucence may also facilitate thermal regulation by allowing heat to dissipate more effectively.'
The correct answer is D) camouflage;.