(B) states "some of the lawyers are not athletes" and is diagrammed as "L - some - not A" Since some statements are reversible, we can also take this to mean "not A - some - L."
(C) states "some of the athletes are not lawyers" and is diagrammed as "A - some - not L." Since some statements are reversible, we can saw "not L - some - A."
Therefore, the difference between the two options are the groups they are discussing. (B) is discussing the group of lawyers and the group of non-athletes; (C) is discussing the group of athletes and the group of non-lawyers. Therefore, the two answer choices have different meanings.
Does this make sense? Please let us know if you have any additional questions.