Please read the forum guidelines before posting: we ask that you cite the source of problems you post. Also, I believe that this problem is from the Official Guide, meaning that it's copyright and we can't reprint it here. However, there is an explanation in the GMAT Navigator app on our website:
https://www.manhattanprep.com/gmat/forums/sviatovin-is-a-medieval-moringian-text-t34650.htmlIt seems that your confusion may relate to the subtle but important distinction between a
strengthener and an
assumption. Take a look at this post here that I wrote:
https://www.manhattanprep.com/gmat/forums/post130517.html#p130517