Hi! This is a Strengthen with Necessary Premise question ("an assumption on which the argument relies").
To answer your more general question (re: learning the skills to better and more consistently distinguish between question stems that include a variant of the word "assumption"), use our Daily Drills! You can find instructions on each of our five Daily Drills here: https://testmaxprep.com/lsat/blog/free-daily-lsat-prep-drills-by-lsatmax.
