PrepTest 109, Section 3, Question 1
North American eastern white cedars grow both on(63 more words not shown)
Which one of the following,(21 more words not shown)
- AThe conditions on(16 more words not shown)
- BIn areas where(15 more words not shown)
- CTrees that are(16 more words not shown)
- DThe roots of(30 more words not shown)
- EEastern white cedar(20 more words not shown)
Reading the argument
The smaller trees are the older ones. Why would the cedars with less access to nutrients outlast the trees growing in good forest soil?
The height difference makes sense on the facts we're given. A tree with better access to moisture and nutrients has more opportunity to grow. But growing taller and surviving longer aren't the same thing. Something could kill a large, healthy tree before it reaches an especially old age.
What if people cut down the forest trees but leave the hard-to-reach cliff trees alone? Or what if a forest fire destroys trees on the ground while the ones on the cliff escape it? Those are possibilities to investigate, not facts we can assume. They would explain how the less favorable growing location could nevertheless offer protection.
What we’re looking for
The question asks us to explain the age difference. I'd look for something that cuts short the lives of forest trees while sparing the cliff trees. We already have an account of why the cliff trees are smaller. We need an account of why more of them have survived for so long.
Working the answers
- A
This compares cliffs with other places that have few tall trees. Our comparison is between cliff cedars and forest cedars, and the difference we need to explain is their ages. Similar growing conditions in a third location don't explain why forest trees die sooner.
- BCorrect
This fits the fire prediction. Forest trees face a relatively frequent threat that the cliff trees escape. Good soil and moisture can help a tree grow, but they won't preserve it if a fire kills it.
The cliff trees can therefore survive through fires that shorten the lives of forest trees. B doesn't need to say every forest tree burns or every cliff tree reaches five hundred. It supplies a reason for the different age patterns we observe.
- C
This applies to old trees generally. If losing bark threatens a tree's survival, we still need to know why that threat has different effects in the forest and on the cliff. C gives no difference between the two locations, so it leaves the comparison unexplained.
- D
This explains why a cliff tree stops getting taller: its roots run out of room. But why should that tree live longer than one in the forest? A limit on height isn't an explanation of the age difference. Don't solve the size question when the stem asks about age.
- E
Furniture-making might remind us of the logging possibility. But E doesn't tell us that forest cedars are cut down more often than cliff cedars, or that harvesting explains the observed ages. Knowing a use for the wood doesn't establish the difference in survival we need.
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