I knew "only if" was going to come back to bite me

Yeah, I was really dissatisfied with the explanation for C. I think in addition to your thoughts in your response, it's also a case of choosing the best response and E directly denies an explicit alternative explanation where C heads off ideas that are a step back from whats in the stimulus, and is maybe less strength?

E: Abnormalities→snoring

C: Age→Abnormalities→and/or→snoring

Weight→Abnormalities→and/or→snoring