PrepTest 144, Section 4, Question 18
For several centuries there have been hairless dogs(72 more words not shown)
Which one of the following(7 more words not shown)
- AHairless dogs have(14 more words not shown)
- BMost of the(13 more words not shown)
- CCenturies ago, no(22 more words not shown)
- DIf hairless dogs(21 more words not shown)
- ECenturies ago, it(19 more words not shown)
Reading the argument
If these dogs didn't develop the rare trait separately, how did they get from one region to the other?
The passage gives us a reason to suspect transport: the dogs weren't wild, and hairlessness was very unlikely to arise independently in both places. It also tells us that the mountainous jungle made travel over land extremely difficult centuries ago. Let's accept that historical difficulty rather than wonder whether the jungle existed then.
A boat trip sounds plausible. I'm less certain about the purpose of the trip. People might transport dogs while exploring or fighting a war, not just while trading. But the author only says a trading expedition was probable. We don't need to eliminate every possible nontrading voyage.
What we’re looking for
The necessary-assumption question asks what the explanation needs. Keep the main inference in view: the author uses difficult land travel to support travel by boat. An answer must supply something that reasoning relies on, rather than add every detail we might want to know about the dogs or the travelers.
Working the answers
- A
The dogs could also have lived in some third place. Nothing in this proposed movement between Mexico and Peru requires them to have been absent everywhere else. A adds a worldwide exclusivity claim.
- B
The route taken by most trade goods doesn't have to match the route taken by these dogs. Even if most goods entered western Mexico over land, these particular animals could have arrived by boat. The argument doesn't need a majority claim about trade as a whole.
- C
“Probably during trading expeditions” doesn't mean nobody ever traveled by boat for another purpose. Other voyages could have involved exploration, war, or ordinary travel. The existence of those trips doesn't rule out the proposed trading expedition.
- D
A dog could accompany a trader without being traded. Perhaps it was a companion kept aboard the boat. The argument suggests a kind of voyage, not that the dogs themselves were exchanged for goods.
- ECorrect
What if the sea route was just as difficult as the route through the jungle, or even worse? Pointing to the difficulty of traveling over land would then give us no reason to favor a boat. The argument relies on the boat route being easier. E provides that missing comparison; it doesn't have to establish why the travelers brought the dogs or what they did with them afterward.
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