All zebras have stripes, and the most widespread subspecies has the best-defined stripes. The stripes must ttherefore be of importance to the species. Since among these grassland grazers the stripes can hardly function as camouflage, they must serve as some sort of signal for other zebras. Which one of the following, if true, most strongly supports the conclusion regarding a signaling function? ['Zebras react much faster to moving shapes that have stripes than they do to moving shapes that are otherwise identical but lack stripes.', 'The subspecies of zebras with the best-defined stripes is also characterized by exceptional size and vigor.', 'In certain tall grasses zebras can be harder to spot than grazing animals with a coat of uniform color.', 'A visual signal transmitted among the members of a species can consist of a temporary change of color perceptible to other members of the species.']