PrepTest 115, Section 4, Question 12
The higher a dam, the more exposed it(49 more words not shown)
Which one of the following,(9 more words not shown)
- AThe higher a(16 more words not shown)
- BArch dams are(16 more words not shown)
- CThe larger the(12 more words not shown)
- DThe basic engineering(17 more words not shown)
- EArch dams under(19 more words not shown)
Reading the argument
Being exposed to more danger doesn't guarantee more collapses. What if the people building the taller dams take extra care precisely because the forces are greater? A structure could face a harder test and still hold up better if it were designed and built more carefully.
The figures make that possibility worth considering. More than half of the arch dams are over 100 meters high, yet all six recent collapses happened among the shorter arch dams. We need to explain why the group exposed to greater forces avoided these collapses while the shorter group did not.
What we’re looking for
My first guess is a difference in construction quality. Perhaps builders put more thought and reinforcement into the taller structures and less into ones they assumed were easier to keep standing. A local event, such as an earthquake affecting particular smaller dams, is another possibility we could investigate. For this resolve question, we're looking for a fact that could offset the taller dams' greater exposure to danger.
Working the answers
- A
We are already comparing arch dams with other arch dams. A says taller dams are more likely to use that design, but it doesn't explain why the shorter members of the arch-dam group accounted for all the collapses. The choice of design isn't the missing comparison.
- B
Cost and complexity relative to other dam designs don't explain the difference between tall arch dams and short arch dams. Even if all arch dams were more expensive than comparable alternatives, we would still need to know why the taller ones held up better in the period described.
- CCorrect
More careful design and construction can compensate for greater exposure to dangerous forces. Treating the taller dams as larger structures, this gives us the construction difference we were looking for: the more demanding projects received more care.
The wording uses “larger,” not “higher,” so we should notice that connection rather than pretend the words are identical. But height is a dimension of a dam's size, and C supplies a relevant reason the tall structures could withstand greater forces. It needn't prove exactly why every collapse occurred to help resolve the apparent puzzle.
- D
Knowing the basic principles for a long time doesn't tell us whether individual dams were designed or built with equal care. Nor does it distinguish the taller dams from the shorter ones. The age of the engineering knowledge leaves the observed difference unexplained.
- E
This again compares arch dams with other designs. Short arch dams could be safer than other short dams and still account for all the collapses among arch dams. We need to compare the short arch dams with the tall arch dams, not with a different type of structure.
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