PrepTest 127, Section 1, Question 11
Studies have shown that the more high-stress points(36 more words not shown)
Which one of the following,(16 more words not shown)
- AIn many structures(17 more words not shown)
- BFractures do not(25 more words not shown)
- CIn many structures,(10 more words not shown)
- DStructures with no(10 more words not shown)
- EImproper bridge construction,(25 more words not shown)
Reading the argument
If a bridge has many points under high stress, I can see why it might be more likely to fracture. I would also expect the fracture to develop where the stress is greatest. But the observation is that bridges fracture somewhere else. Why does the problem show up away from the points that made us worry?
The location is the puzzle. We do not merely need a reason bridges sometimes break; we already know that they do. We need to understand why more high-stress points predict trouble while those points are not where the fractures develop.
What we’re looking for
Perhaps pressure gets diverted to other parts of the bridge. Or perhaps those other parts have some vulnerability that the high-stress points do not. For this explanation question, I would look for something that makes the unexpected location understandable. A fact about how common bridge failures are would not be enough.
Working the answers
- A
This repeats a similar observation for ships and airplanes. Even if the pattern occurs in several kinds of structures, we still need to know why it occurs. Another example of the puzzle does not supply its explanation.
- BCorrect
The high-stress points have been reinforced, so those locations have protection against fracturing. But the stress has not simply disappeared: it is transferred to other points, where it causes fractures.
That connects both sides of the observation. High stress still creates a danger for the bridge, but reinforcing the expected trouble spots changes where that danger produces a break. The points we initially expected to fracture are protected, while the transferred stress can damage other parts.
- C
This explains how a fracture might create high-stress points. Our question concerns why the fracture develops away from the existing high-stress points. Reversing which event produces the other does not explain that location.
- D
Structures without high-stress points are outside the comparison we need to explain. They might fracture for another reason, but that does not tell us why bridges with high-stress points fracture somewhere else.
- E
Poor welding or inferior steel might explain why a bridge has both high-stress points and a high chance of fracturing. But where will it fracture? E never explains why the failures occur away from the high-stress locations. B adds the reinforcement and transfer of stress needed to answer that question.
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