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The stimulus says that a running track with a hard surface is better for inducing quicker times than a soft surface, because a runner's foot will be in contact with the hard surface for a shorter period of time.
The problem I have with this one is how the question stem is phrased. If I am looking for an answer choice which shows the above explanation to be only a partial one, then (C) is obviously the answer.
But what if this was just a classic weaken question, meaning the question stem explicity said to "cast doubt on the argument?" In that case, wouldn't (C) actually be a strengthener? The way I see it, the conclusion is that hard surface is better for speed. So (C) supports that statement by giving another reason how hard surface enhances a runner's speed.
I guess the reason I'm asking this is because I'm not sure what to weaken: the conclusion (that hard tracks are faster) or the entire argument (hard tracks are faster because the foot is in contact with the surface shorter).

Thank you.

I hate this question. I got it wrong the first time I tried it, and it's deceptively difficult. This is a weird question type which could either been a weaken or strengthen depending on how you look at it. You could think of it as aiding the explanation or revealing an alternative explanation.

A - is incorrect because the stimulus qualifies "under dry conditions." We're not concerned about scenarios in which there are wet conditions - it's totally out of scope.

B - distinguishes between runners and not tracks. Does runner height apply to only indoor hard tracks? No it doesn't, so this distinction is out of scope and irrelevant.

C- is correct. It clearly states another alternative reason that hard tracks lead to fast running speeds.

D- This one is really, really tricky. But it fails to distinguish between hard and soft tracks. How do we know the fastest tracks in the world are hard surfaces? We don't, so we can't say this is the extra explanation the stimulus needs.

E- Who cares if the two tracks need different maintenance procedures? How does this affect track speed of hard surfaces? This answer choice is too bare to provide anything to bolster the explanation and plus we're only really concerned about hard tracks.

It is a strangely-worded question. More or less, treat it like a weakener - identify the core of the argument, find the assumptions, find an answer that addresses one of them (so, in a sense, you're right, it points out what would strengthen it). Here's a full write-up of that question - tell me if you have more questions: http://www.atlaslsat.com/forums/preptes ... 4d4e37ec21