PrepTest 156, Section 2, Question 7
Mr. Xu: The arctic squirrel gets so cold(97 more words not shown)
Ms. Yerky's response proceeds(1 more words not shown)
- Apresenting evidence that(8 more words not shown)
- Bshowing that the(12 more words not shown)
- Coffering an alternative(16 more words not shown)
- Dshowing that a(8 more words not shown)
- Eshowing that the(13 more words not shown)
Reading the argument
How does blood stay liquid when it is colder than water's freezing point? Mr. Xu proposes a substance in the squirrel's blood that prevents freezing. That's one possible account, but I want to know why it must be the explanation.
Could something about the blood circulating inside a living animal matter? That's a possibility to investigate, not a fact we've established about freezing. Keep it separate from what Ms. Yerky actually says.
Yerky brings in a laboratory test: outside the animal, squirrel blood freezes at the same temperature as water. She uses that result to argue against the proposed antifreezing substance. If the blood contained the substance Xu describes, we'd expect the blood in the vial to resist freezing too. The observed result gives her evidence for the opposite conclusion.
What we’re looking for
The question asks how her response works. I'd describe it as introducing experimental evidence against Xu's explanation. We don't have to supply a replacement explanation to recognize that move.
Working the answers
- ACorrect
Xu says the blood must contain a substance that prevents freezing at water's freezing point. Yerky says it contains no such substance and supports her position with the vial experiments. Those conclusions conflict, and the new evidence is meant to support Yerky's side.
- B
Yerky never says Xu measured the squirrel's body temperature badly or used unreliable methods. She introduces another experiment. Challenging a conclusion with new evidence is different from showing that the earlier evidence was collected incorrectly.
- C
This may sound familiar because we wondered whether circulation inside the animal could matter. But that was our suggestion, not Yerky's. She attacks the substance explanation without telling us what does keep the squirrel's blood from freezing. Don't give a speaker credit for an explanation we supplied ourselves.
- D
Nobody argues over the meaning of 'blood,' 'freezing,' or another key term. Yerky's objection concerns what happens in a laboratory experiment, not an unclear definition. There's no dispute about the meaning of the words that could support this description.
- E
Xu's observations are relevant: the failure of the squirrel's blood to freeze is exactly what needs explaining. Yerky doesn't dismiss that evidence as unrelated to the issue. She adds evidence that calls Xu's particular explanation into question.
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