[quote="ziyuen"]A high school has found that, for each of the last 15 years, the average grade point average for members of the cross-country running teams has exceeded the average grade point average for the school as a whole. This phenomenon can most likely be attributed to the fact that long distance runners have so much time to think while running that they can essentially study as they run.

Which of the following most undermines the conclusion drawn above?

A. Cross-country running is more strategic than many realize, requiring runners to expend mental energy thinking about race tactics.
B. Many cross-country runners are also members of the track-and-field team, for which the average grade point average is actually lower than that of the school as a whole.
C. The cross-country team is among the few teams that do not require a try-out, making it a popular activity for high-achieving students who want to list a sport on their college applications.
D. Because the nearest cross-country trails are a long distance from the school, cross-country is one of the most time-consuming activities the school offers.
E. The cross country team's average grade point average has dropped each of the last three years.

C it is ----The student in cross country is already high achievers ...

A is a trap here.
Surely, people will look for a reverse causal relationship, but A talks about mental energy for tactics. => A is out.
B is just merely a correlation.

C tells that students with good grades join the run, not the other way.

VERITAS PREP OFFICIAL SOLUTION:

This weaken problem features a common gap in logic: a fact is given (the cross-country GPA is higher than the average GPA) and then one plausible explanation is given as the only explanation for why that fact is true. This is essentially mixing correlation for causation: because two things occur together (runners have a lot of time to think, and runners have high GPAs, the time to think must cause the GPA). The best ways to weaken one of these arguments are to find an alternate explanation or to show that the causation is reversed (it's not that time spent running causes the high GPA, but rather the high GPA leads people to run).

And choice C does exactly that - it suggests that students with high GPAs are more likely to join the cross-country team. It's not that the running makes them better students, but instead good students tend to go toward running as a way to add an extracurricular activity to their application profile. That's why choice C is correct.

Among the wrong choices:

Choice A should be tempting, but it does not directly attack the notion that runners have a lot of time to think. An activity can be strategic and still allow time to think. Choices B, D, and E each try to attack the premise, making you think that the GPA shouldn't be as high as it is. B does this by grouping cross-country runners with the other track-and-field athletes, for whom the GPA is lower. But we already know that the cross-country GPA is high, so it doesn't matter which other groups you could pool them with to lower their grades. Choice D similarly tries to provide a reason why you wouldn't think that the GPA would be high (it's such a time-consuming activity!) but again that doesn't matter - the GPA is high, so we're just trying to determine the cause. And choice E tries to do this by showing that the GPA is dropping, but again it's already been established that it's higher than average, and your only job is to determine why.
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