Question 30·Hard·Central Ideas and Details
In a 2021 study, ecologists monitored urban beaver (Castor canadensis) colonies along a 40-kilometer stretch of the Riverton River, which flows through both industrial areas and parkland. Using motion-sensing cameras, the researchers documented 112 individual beavers over twelve months. They found that beavers built 19 dams within city limits, all located within 200 meters of public green spaces, and that nocturnal activity at these dams peaked between midnight and 4 a.m.
Along rural stretches of the same river, beaver activity was distributed more evenly throughout the night and day, and dams were spaced an average of 2 kilometers apart.
The researchers concluded that the urban beavers’ construction patterns likely reduce encounters with humans and domestic dogs while maximizing access to preferred forage found in landscaped parks.
Which choice best states an inference about the urban beavers studied that is supported by the passage?
For inference questions about studies, underline (1) the reported findings (locations, timings, quantities) and (2) any stated conclusion explaining those findings. Then choose the option that paraphrases the conclusion while staying within the data—avoid choices that introduce unstated measurements, comparisons, or prioritized causes.
Hints
Focus on the conclusion sentence
Reread the last sentence that begins with “The researchers concluded…” What two main reasons do the researchers give for the urban beavers’ construction patterns?
Pay attention to location details
Look at where the 19 urban dams are located. How close are they to public green spaces, and what might those green spaces contain that beavers like?
Watch for overstatements
If a choice turns a trend into an absolute (for example, changing “peaked” into “only” or “most”), it’s likely not supported.
Don’t add unstated comparisons
Be careful about choices that compare urban and rural patterns (like spacing or how restricted the activity is) when the passage doesn’t quantify those comparisons for the urban dams.
Step-by-step Explanation
Understand what the question is asking
The question asks for an inference best supported by the passage. Choose the option that is strongly grounded in what the passage states or clearly implies, without adding details or making the passage’s claims more extreme than they are.
Locate key information about urban beavers
Key urban details:
- 19 dams within city limits
- All urban dams were within 200 meters of public green spaces
- Activity at these dams peaked between midnight and 4 a.m.
Use the researchers’ conclusion
The conclusion explains why the patterns likely occur: they reduce encounters with humans/dogs while maximizing access to preferred forage found in landscaped parks. That directly links dam placement near parks/green spaces with access to food.
Match the best-supported inference
The choice that most directly reflects the passage’s location data (dams near green spaces) and the researchers’ explanation (access to preferred forage in parks) is:
“They concentrate their dam-building efforts near parkland to exploit abundant vegetation.”