PT23 · S2 · Q8 The caterpillar of the monarch

Already Acknowledged by Author Too Weak: some The paragraph only said that monarchs were poisonous to "many" predators, so he's allowed for the possibility that monarchs (and other milkweed eaters) aren't poisonous to all predators. Since some only means "there is at least one predator that doesn't have a toxic reaction to milkweed insects", it's unlikely to be a correct answer on question types like Strengthen / Weaken / Paradox, where we want the most impactful answer.

The author is thinking that viceroys are not poisonous. Any of them. Meanwhile, he thinks that monarchs are poisonous (presumably most / all of them). The author thinks that what is protecting individual viceroy butterflies is the fact that they look like a different species, in which most members are toxic to predators. In order for this answer to apply to what we know of viceroys, we'd have to rewrite it like Being very visually similar to a species whose members are toxic to many predators will not protect butterflies unless .... That would at least be referring to viceroys, and then it could say something that would undermine the author's hypothesis about visual resemblance to monarchs being the viceroy's shield against predators.

This affirms something the author is assuming. If none of the viceroy's predators matched the monarch's predators, that would hurt the author's hypothesis. He thinks that predators are scared from viceroys because they think, "Oh, it's one of them nasty monarchs I've tried eating before".

This answer is saying it's actually pretty rare for a butterfly species to protect itself via being toxic to predators. This makes us more inclined to believe that the viceroy is seldom preyed on, not because it's toxic to predators, but because it looks very similar to one of those rare butterfly species (the monarch) that is toxic to predators.