PrepTest 135, Section 1, Question 19
Last winter was mild enough to allow most(57 more words not shown)
Which one of the following,(10 more words not shown)
- AIncreases in bird(7 more words not shown)
- BWhen birds do(17 more words not shown)
- CBirds eating at(11 more words not shown)
- DBirds that remain(14 more words not shown)
- EBirds sometimes visit(15 more words not shown)
Reading the argument
Avoiding a dangerous trip could leave more birds alive. The argument already gives us a sensible reason why a mild winter might increase the next year's population: many birds stayed put instead of migrating, so fewer were lost during migration. That's what “attrition” means here.
Still, could something else explain the larger population? Perhaps there was an independent increase in breeding. The proposed explanation is plausible, but I'd welcome more evidence tying the increase to the winter conditions.
One useful prediction would be a repeated pattern: mild winters are followed by larger bird populations. Another would explain an additional benefit of staying put. Maybe the birds breed more, or more young survive. Those possibilities would give the weather a clearer connection to the population increase.
What we’re looking for
We're strengthening this explanation, so we don't need to show the weather was the only influence. We need evidence that makes its contribution more convincing.
Working the answers
- A
Unusual weather is broader than a mild winter. The answer doesn't tell us which unusual patterns precede population increases or why. It offers a loose association, but it doesn't connect the particular winter conditions here to the outcome as directly as C does. “Sometimes” isn't automatically disqualifying; the problem is how little this unspecified pattern tells us about this case.
- B
Different mating behavior could lead to more offspring, fewer offspring, or no change in the number. I'd like evidence of more successful breeding, but this answer stops at a difference. We can't supply the favorable direction ourselves.
- CCorrect
This develops the feeder detail rather than my predictions about breeding. The mild winter let birds forage naturally, so fewer visited feeders. If feeder visitors are more vulnerable to predators, that shift provides another reason more birds might survive.
Now the mild winter has two plausible routes to the larger population: fewer migration losses and less exposure to the particular predation risk associated with feeders. Naturally foraging birds aren't immune to predators; they are less vulnerable by the comparison C gives us.
- D
Running out of food before spring would create a problem for birds that stay in their summer range. That could reduce survival and work against the proposed population benefit. It doesn't strengthen the explanation.
- E
Some birds may visit feeders even when natural food is sufficient. That is compatible with fewer birds using feeders during the mild winter. It doesn't tell us whether the winter improved survival or reproduction, so it supplies no useful additional link to the population increase.
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