The question stem for this question asks us to pick an answer choice that shows that the explanation we were given in the stimulus is only a "partial one." I was doing this question as part of my weakening problem set. I read through the stimulus and was quickly able to identify my premise and conclusion:

P: Time runner's foot spends on the surface is less on a hard surface

C: Hard surface makes for greater running speed than a soft surface

I ended up choosing answer choice B, because I thought it provided us with an alternative explanation for why runners perform faster on the hard surface. In my mind, I thought the author was neglecting to acknowledge that it was actually the height of the runners that was affecting their performance rather than the hard surface.

If I were to add the following to answer choice B:

"when running on hard surfaces"---- would this make answer choice B correct? If not, why? Or would the stimulus have to make reference to the short v. tall runners?

Admin Note: https://classic.7sage.com/lsat_explanations/lsat-30-section-2-question-09/