Self-study
For several centuries there have been hairless dogs in western Mexico and in coastal Peru. ██ ██ ████ ████████ ████ █ █████ ██ ████ ██ ████████████ ███████ ██ ███ ████████ ██████████ █████ ███ ████ ████ █████ ███████ ██ ███ █████ ███ ███ ████ ███████████ ██████ ██████████ █████ ███ ███████ █████ ████ ████ ████████ ██████ ███████ ████ █████████ █████████ █████████ ████ ███ ████ ████ ████ ████ ███████████ ████ ███ ██ █████ ███████ ██ ███ █████ ██ █████ ████████ ██████ ███████ ████████████
Summary
The hairless dogs in Mexico and Peru must have been transported by boat from one of those two countries to the other, and probably during trade.
Why must they have started in either Mexico or Peru? Well, they wouldn’t have just turned up out of nowhere in both countries. Hairlessness likely didn’t originate twice, so both sets of dogs probably originated a single place.
Why must they have come by boat? They’ve never existed in the wild, so to arrive anywhere else, they must have come with humans. And overland travel between Mexico and Peru was very difficult back when these dogs appeared in those countries.
Notable Assumptions
The author hypothesizes that boats are the answer because overland travel would have been so difficult. But he never says whether boats were any easier. He’s implying a comparison (overland harder, boats easier) without actually supporting that comparison. So he must assume that travel between the two countries was indeed easier by boat than by land.
He also assumes that the dogs weren’t transported to both Mexico and Peru from some other location(s).
18.
Which one of the following ██ ██ ██████████ ████ ███ ████████ █████████
a
Hairless dogs have █████ ████ █████ ████████ ██████ ██ ███ ███████ ██ ███████ ██████ ███ ███████ █████
The author assumes the dogs weren’t transported to both Mexico and Peru from some other location(s). But he doesn’t assume they’ve never been found anywhere else. What if they were transported from Mexico to Peru, and then to Argentina? That wouldn’t damage the argument.
b
Most of the █████ █████ ████ ████ ████ ███████ ██████ █████████ ███ ████ ███████████ ██ █████
Too strong. The author doesn’t need to assume that most trade from all places to Mexico was by boat. He just needs to assume that there were at least some trade expeditions running between Mexico and Peru.
c
Centuries ago, no ███ █████ ████ ████████ ███████ ███████ ██████ ███ ███████ ████ ██ ████ ██████ ███ ███ ████████ ██ ████████ ███ █ ███████ ███████████
Too strong. The author doesn’t need to assume that all boat travel was for trading expeditions—just that at least some boat travel was (enough to make it likely that the dogs were on some of those expeditions).
d
If hairless dogs ████ ██ ███ ████ ███████████ ███████ ███████ ██████ ███ ███████ ████ ██ █████ ████ ████ ██████ ██ ████████ ███ █████ ██████
Whether the dogs were traded during trade expeditions is irrelevant. The author merely assumes that there was some way for the dogs to be present on those expeditions. Perhaps they were brought as gifts rather than exchanged, or perhaps they were there by accident.
e
Centuries ago, it ███ ██████ ██ ██████ ██ ████ ███████ ███████ ██████ ███ ███████ ████ ████ ██ ██████ ██ ██ ████████ ██████
The author implies a comparison between overland and boat travel but never says how difficult boat travel was. He must assume boat travel was easier. Otherwise, if it was just as hard or harder than overland travel, the conclusion becomes unsupported or even anti-supported.