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Question
QuickView
Choices
Curve Question
Difficulty
Psg/Game/S
Difficulty
Explanation
PT92 S1 Q07
+LR
Strengthen +Streng
A
7%
154
B
3%
151
C
89%
161
D
1%
145
E
1%
148
121
133
146
+Easiest 147.037 +SubsectionMedium

This is a Strengthen question.

The argument uses causation logic. The stimulus begins and ends with two parts of a hypothesis (a causal conclusion): first, that large trucks are not causally responsible, and second, that studded snow tires are causally responsible for ruts in the transportation official’s city.

Why should we believe this? The premises state that out of the many places that have roughly as much large truck traffic as the official’s city does and also a comparable amount of snowfall, only the few places that allow snow tires have ruts in them. This looks like the results of a controlled experiment. All else held equal, we toggle only snow tires. With snow tires, ruts. Without snow tires, no ruts.

What clearly follows from the premises is that snow tires are causally necessary since without them there are no ruts. What also follows is that large trucks are not causally sufficient since there are cities with large trucks but no ruts. Had the author reached either or both of those conclusions, the argument would be fine. But he reached a far less nuanced conclusion, one that shifted the causal blame entirely away from large trucks (yet we only know that large trucks are insufficient, not that they’re without any causal impact) and entirely onto studded snow tires (yet we only know that snow tires are causally necessary, not that they’re sufficient). Another way to understand why the argument is problematic is to consider the alternative hypothesis that also fits with the facts: both the snow tires and the large trucks have to act together to cause ruts.

Look again at the premises and notice that the facts so far fit with both the author’s hypothesis (snow tires only) and the alternative hypothesis (snow tires plus large trucks). That’s because large trucks were present in all the cities considered. We simply toggled on and off the presence of snow tires. With snow tires toggled on we find ruts, with snow tires toggled off we find no ruts. The only hypothesis excluded is the large truck only hypothesis, which is another way of saying that large trucks are not causally sufficient.

So how do we decide between the snow tires only and the snow tires plus large trucks hypotheses? Lucky for us, they make different predictions. In cities that have snow tires but no large trucks, the snow tires only hypothesis would predict ruts while the snow tires plus large trucks hypothesis would predict no ruts. Seeing what actually happens in those cities will help us decide between the two hypotheses.

This is exactly what Correct Answer Choice (C) does for us. It says that most of the places that allow snow tires yet don't have large truck traffic have ruts. This fact confirms the prediction of the snow tires only hypothesis and rules out the snow tires plus large trucks hypothesis.

Answer Choice (A) says large trucks are not allowed to have studded snow tires in many areas. This was close but also so very far. With a tiny tweak, (A) could also have ruled out the combination hypothesis. We just needed to say that in those areas that allow snow tires, large trucks are not allowed to have snow tires. That means the ruts observed in the stimulus in the cities that allowed snow tires definitely did not come from large trucks with snow tires, on the assumption that the large trucks were not in violation of this ordinance. It means that the ruts came from other snow-tired vehicles. That means it is the snow tires and not large trucks that are causally responsible for the ruts.

Answer Choice (B) says the number of ruts in the roads of the official's city has declined recently as the amount of large truck traffic has diminished. This correlational phenomenon is inconsistent with the causal hypothesis in the argument. If it's true that large trucks don't cause ruts then we wouldn't expect to see any difference in the number of ruts as large truck traffic either increases or decreases. Because (B) disconfirms that prediction, it weakens the argument.

Answer Choice (D) says some cities with even more truck traffic than the official's city also have ruts in their roads. This is useless because we don't know whether those cities allow snow tires.

Answer Choice (E) says most places that have little snowfall do not allow the use of snow tires. That makes sense. But it's not clear how this has anything to do with the argument. We don't know whether those places have large truck traffic nor do we know whether they have ruts in their roads.