LR Drill Set 12, Question 10
In most seas, shipworms are by far the(60 more words not shown)
Which one of the following(8 more words not shown)
- ANo natural predators(6 more words not shown)
- BThe Baltic Sea(11 more words not shown)
- CHigh salinity levels(14 more words not shown)
- DWater with a(20 more words not shown)
- EMost recoveries of(21 more words not shown)
Reading the argument
Getting rid of the shipworms sounds good for a wooden ship. But what else changes when the water is less salty?
The Baltic's low salt level keeps shipworms from surviving there. Since those creatures are the most common cause of decay in most seas, removing them gives us a sensible reason to expect better preservation. The argument isn't baseless.
Still, the salt might affect the wood directly as well as affecting the worms. Suppose very salty water greatly slows the damage water itself does to wood. In that case, the ships in other seas would have a protection that the Baltic ships lack. The absence of worms wouldn't settle which ships end up in better condition.
What we’re looking for
The question asks for something this comparison depends on. My prediction is that the lower salt level doesn't bring a decay problem that undermines the advantage of losing the worms. “All else being equal” doesn't remove this concern: salt level is one of the differences the argument itself introduces.
Working the answers
- A
Shipworms could have natural predators and still be the most common cause of decay. A predator needn't eliminate every shipworm. The argument requires the stated damage from worms, not a world in which nothing eats them.
- B
The Baltic only needs to be below the level at which shipworms can survive. It doesn't have to be less salty than every other sea. Another sea could have an even lower salt level without changing the argument's comparison with most other seas.
- CCorrect
This rules out a strong protective effect of high salt levels: drastically slowing the decay caused by water. If high salinity supplied that protection, taking the salt away would have a downside as well as the benefit of removing shipworms. The argument depends on not overlooking that competing effect.
Be careful about the strength of this assumption. C doesn't say salinity has absolutely no effect on decay. It denies a drastic slowing effect that would threaten the comparison. We don't need to turn that into the broader claim that salt is completely irrelevant.
- D
The argument doesn't need ordinary seawater to cause no decay on its own. Water could contribute some damage while shipworms remained the main problem. For example, the water-related damage could be similar in both settings, with extra damage from worms elsewhere. D removes a cause of decay altogether; the argument only needs the predicted advantage for Baltic ships.
- E
Where people recover ships doesn't tell us the relative condition of similarly aged ships underwater. Recovery might depend on access, interest, or many other factors. The argument concerns preservation in different waters, not which wrecks people usually retrieve.
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