Let's start with the passage. The author tells us that since one ingredient has no effect on its own, that if we find the other ingredient also had no effect on its own, then the product has no effect. This is flawed since a thing can be more than the sum of its parts. The product may still be effective if the ingredients combine to have an effect that they would not have had on their own. This is what A says, but in obnoxiously abstract words.