http://classic.7sage.com/lsat_explanations/lsat-60-section-1-question-24/
Okay, so perhaps I'm overthinking this, but here goes:
I put down (B) rather than (C) for the following reason: the stimulus indicates that the degree of immuno-effect is related to branching of the beta-glucans, but states that beta-glucan extracts from the shrooms have this effect (i.e. Whether b-g 's in general do is not stated). Thus, to say that b-g branching triggers immuno-effects in mammals (answer C) seems to overshoot what's in the passage, whereas (B), which only mentions that if extracts have an immuno-effect, then that shroom must be making b-g 's.
Tell me where i'm going wrong.
Thanks & all the best w/ practice,
Z