PrepTest 148, Section 4, Question 7
Although some animals exhibit a mild skin reaction(54 more words not shown)
Which one of the following,(12 more words not shown)
- AWood rats build(9 more words not shown)
- BA number of(11 more words not shown)
- CIt is common(9 more words not shown)
- DIn approximately 85(14 more words not shown)
- EPoison oak and(14 more words not shown)
Reading the argument
A defense doesn't have to bother every animal equally. Could the painful human rash be part of its protective effect? Could even a mild reaction discourage some other animals? The fact that humans react more strongly doesn't, by itself, show that the oil evolved for some purpose other than defense.
The wood rats make the author's case more interesting: they use poison oak branches in their nests, so they evidently tolerate that contact. But tolerating the branches doesn't necessarily mean feeling no irritation, and it doesn't tell us how every other animal responds.
What we’re looking for
To strengthen the argument, my first thought is to connect the premises to that evolutionary conclusion: show that an oil tolerated by these animals would not have evolved as a defense. That would give the author the missing step. We have evidence about the animals' reactions, but the conclusion goes further and tells us why the oil probably evolved.
Working the answers
- A
Dead branches might differ from live ones, but A doesn't say whether they contain the oil or how much contact the rats have with it. We shouldn't assume dead, brittle wood is free of urushiol. Without that connection, the nest material doesn't give us stronger evidence that the oil lacks a defensive role.
- BCorrect
Several kinds of animals eat the plants. That makes the proposed defense look less effective against an obvious threat: being eaten. The evidence goes beyond animals merely tolerating contact with nest branches; animals actually use the plants as food.
This doesn't prove that no animal is deterred or settle exactly why the oil evolved. It is still useful support for the conclusion that chemical defense may not explain it. We don't need the answer to close every gap to recognize that B helps the argument.
- C
Other plants commonly use chemical defenses. That makes chemical defense a familiar possibility, but it doesn't show that this particular oil evolved for another purpose. We need evidence about urushiol's role, not the general popularity of chemical protection among plants.
- D
This adds detail about the human reaction. It doesn't show that the oil wasn't a defense; a rash affecting many humans is compatible with a deterrent effect on humans. The percentage alone doesn't answer the question about the oil's evolutionary role.
- E
Growing well in human-altered habitats doesn't tell us why the oil evolved. Those places could offer favorable growing conditions for reasons unrelated to urushiol. E doesn't connect the plants' success in that environment with whether the oil serves as a chemical defense.
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