Spiders of many species change color to match the pigmentation of the flowers they sit on. The insects preyed on by those spiders, unlike human beings, possess color discrimination so acute that they can readily see the spiders despite the seeming camouflage. Clearly, then, it must be in evading their own predators that the spiders' color changes are useful to them. Which of the following, if true, most strengthens the argument? ['Certain animals that feed on color-changing spiders do so only sparingly in order to keep from ingesting harmful amounts of spider venom.', 'The color discrimination of certain birds that feed on color-changing spiders is no more acute than that of human beings.', 'Color-changing spiders possess color discrimination that is more acute than that of spiders that lack the ability to change color.', 'Among the animals that feed on color- changing spiders are a few species of bat, which find their prey through sound echoes.']