Danny’s explanation, particularly the last paragraph, is very good; I always tell students to be suspicious of the word “many.” For instance, you probably think that smoking causes cancer; the (accurate) observations that “Many” people smoke and don’t get answer, and “Many” people who don’t smoke still get cancer probably don’t change your mind.
However, one quick correction/clarification – on the LSAT, “some” doesn’t have to be plural. “Some” means at least one, not necessarily “more than” one.