Question 128·Medium·Boundaries
After months of fieldwork, the ecologists' findings on urban wildlife corridors—detailed maps of animal tracks, motion-sensor photographs, and _____—reveal how squirrels, foxes, and even deer navigate city streets.
Which choice completes the text so that it conforms to the conventions of Standard English?
For SAT punctuation and boundaries questions, first identify the main clause (subject + verb) and then see how commas or dashes set off extra information. When you see dashes around a phrase, treat that phrase as a removable chunk and check its internal structure: if it contains a simple list, use normal list punctuation (commas between items, no extra marks right before the closing dash). Eliminate any option that creates doubled or unnecessary punctuation (like comma+dash, semicolon+dash, or double dashes).
Hints
Notice the role of the dashes
Find the two dashes in the sentence. What part of the sentence do they set off, and how does that part relate to "the ecologists' findings"?
Look at the list inside the dashes
Inside the dashes, read the items around the blank: "detailed maps of animal tracks, motion-sensor photographs, and _____." How are the first two items separated from each other?
Think about punctuation at the end of a list
In a normal three-item list with commas and the word "and," do you usually put any punctuation after the last item, right before the sentence continues?
Check for unnecessary or doubled punctuation
Consider what happens if you put a comma, semicolon, or dash right before the existing closing dash in the sentence. Does that create extra or awkward punctuation?
Step-by-step Explanation
Understand the sentence structure
Locate the main subject and verb: "the ecologists' findings … reveal". Everything between the two dashes (from "detailed maps" to the word that fills the blank) is extra information describing those findings. The dashes set off an interrupting phrase that renames or explains "findings."
Identify the pattern inside the dashes
Inside the dashes, you have a list: "detailed maps of animal tracks, motion-sensor photographs, and _____". This is a series of three parallel noun phrases describing types of evidence the ecologists collected. In a standard list, items are separated by commas, and the final item usually comes after "and" with no extra punctuation after it.
Apply punctuation rules for lists within dashes
Within a simple list like this, commas separate the items, but you do not add a comma or semicolon right before the closing dash, because the dash itself already marks the end of the interrupting phrase. So the third item in the list should flow directly into the closing dash without any extra punctuation in between.
Match the correct punctuation to the choices
You need the version of the phrase that has no punctuation after the words before the closing dash. That choice is "acoustic recordings" (choice B).