[prospective2017]

I’m having difficulty understanding the correct answer in Preptest 56, Section 2, Question 8. (A Weaken Question… I’ve been struggling with Strengthen/Weaken in general)

I got down to A and D via the elimination process, but ultimately chose A which is incorrect (D is correct). I thought D was incorrect because it says there “are no” sources, but I figured it was irrelevant whether or not there are any sources north now since the glacier was formed previously. Maybe all the sources that existed north went South so there no sources left north currently, and still could have formed the glacier in question! I was hesitant about the “most” in A but chose it by eliminating D.

Thank you in advance – also I would like to say I am studying for a retake in September after taking it in June and although I was relatively satisfied with my June score, I have had a positive experience studying for the retake and improving on my conceptual understanding by choosing The Trainer and am recommending it to everyone!

[dannypearlberg]

(A) is bad because “most” can mean just over 50%- it doesn’t weaken the argument at all to know that just over 50% of the boulders haven’t been moved more than 100 miles, because that means that just under 50% HAVE been moved more than 100 miles.

(D) does weaken the argument a bit- if there ARE no geological sources of volcanic rock north of this boulder, it seems likely that there WERE none there during the last ice age. True, this answer choice doesn’t rule out the possibility of there being some geological sources of volcanic rock north of this boulder during the last ice age, but that’s ok- it still weakens the argument by telling us that it is likely that there weren’t any.