PrepTest 130, Section 4, Question 11
Researcher: This fall I returned to a research(47 more words not shown)
Which one of the following(8 more words not shown)
- AOf the armadillos(20 more words not shown)
- BMost of the(12 more words not shown)
- CPredators did not(12 more words not shown)
- DThe tags identifying(13 more words not shown)
- EA large majority(26 more words not shown)
Reading the argument
Finding an armadillo in the same place twice does not tell us where it went between those visits.
The researcher tagged the animals in spring and recaptured them in fall. What if they traveled a hundred miles during the summer and then came back? Imagine checking a migratory animal's location only when it has returned to its seasonal home. Repeatedly seeing it there would miss the journey.
That is the problem with using nearby recaptures to conclude that armadillos do not move rapidly into new territories. The evidence gives us two locations at two times, not a continuous record of the animals' movements.
What we’re looking for
A required assumption can protect the argument against that objection. I would look for something ruling out the possibility that the nearby animals generally went away and returned. We do not have to assume that every armadillo stayed perfectly still.
Working the answers
- A
The researcher need not have tagged almost every armadillo in the area. A smaller sample could still provide useful evidence. Whether few animals escaped initial tagging does not resolve where the recaptured animals went during the summer, and that high tagging rate is not required by the inference.
- B
The argument does not require most tagged animals to go missing. That would raise an additional question about whether the recaptured animals represent the others. The missing animals might have moved away, although non-recapture alone would not prove that. B is not a needed assumption supporting the conclusion.
- C
Some tagged animals could have been killed while the surviving sample still provided evidence about movement. The argument does not require the complete absence of predation. Saying no tagged animal was killed is much stronger than the reasoning needs.
- D
Tags do not have to be impossible to remove. It could be possible for an armadillo to remove a tag while enough tagged animals retained theirs to be identified. The possibility of removal is different from a demonstrated problem with these recaptures.
- ECorrect
This blocks the out-and-back explanation for a large majority of the recaptured animals. If that majority actually entered new territory during the summer and returned by fall, finding them near their tagging sites would be poor evidence that they do not move rapidly into new territories.
E does not prove that every animal remained at its tagging site, nor does it settle every possible concern about the research. It supplies a needed defense against the particular gap between being found nearby and having stayed nearby.
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