PrepTest 106, Section 2, Question 13
Mature white pines intercept almost all the sunlight(73 more words not shown)
Which one of the following(5 more words not shown)
- Athe ages of(28 more words not shown)
- Bthe land on(24 more words not shown)
- Ccompetition among the(19 more words not shown)
- Dother species of(15 more words not shown)
- Eany differences in(19 more words not shown)
Reading the argument
The mature trees are making it difficult for the next generation to get started. Their height and foliage keep almost all the sunlight from reaching the ground, even where there are gaps. A new white pine cannot regenerate in that shade.
A “stand” is a group of trees. Here the group consists entirely of mature white pines. My first prediction would concern what can grow beneath them: new white pines won't keep appearing under that canopy. Be careful about the scope, though. The passage gives this restriction for white pines, not for every possible kind of plant.
What we’re looking for
We need to complete the argument with a reasonable inference. The words “a fair bet” allow a supported expectation rather than a claim that every conceivable exception has been ruled out. Keep the barrier to new white pines in mind as we look for the answer.
Working the answers
- ACorrect
This takes our prediction about new trees and uses it to work backward to the ages of the existing trees. Once the older white pines matured and shaded the ground, much younger white pines could not keep starting underneath them. The trees in the stand therefore likely got started within a limited window, before the earlier trees created that barrier.
Imagine, just to make the timing concrete, that a white pine takes 20 years to mature. Trees starting around the same period could all become part of the eventual mature stand. But a fresh generation starting many decades after the first trees matured would face the shade that prevents regeneration. That is why we wouldn't expect the existing trees' ages to be spread over far more than a maturation period.
The answer doesn't say they are all exactly the same age. It gives a rough limit on how far apart their starts are likely to have been, which fits the passage's qualified conclusion.
- B
Enough light for young white pines doesn't require land cleared of every tree. Other trees might have been sparse or might not have created the same blocking conditions. The passage tells us what mature white pines do in a stand; it doesn't establish that bare land is the only place their seedlings can start.
- C
The problem described is a barrier to new white pines beneath the canopy. It doesn't establish that the mature trees are about to kill one another through competition. We have no basis for either that cause of death or the prediction that it will happen soon.
- D
We aren't told how other tree species respond to these conditions. Some might be able to grow in the shade; others might not. The passage doesn't establish that they will arrive soon, much less replace every white pine. The inability of white pines to regenerate doesn't supply that entire forecast.
- E
Age could affect height without being its only cause. The passage doesn't rule out differences in growing conditions or other factors. Knowing that mature white pines grow very tall doesn't let us explain every height difference solely by age.
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