http://classic.7sage.com/lsat_explanations/lsat-33-section-3-question-21/

I dismissed A right off of the bat because I've grown skeptical of the word every.

I see now that it makes sense because for Sufficient Assumption Questions you need to find the Answer Choice that GUARANTEES the outcome, so A works. It may be extra strong, but that's ok.

I should have also had my eyes peeled more for tricky answer choices because it is Q. 21