The mimosa tree evolved in East Africa, where the beetle Bruchidius terrenus preys on its seeds.

Choice B is the best answer because it most accurately describes the function of the third sentence within the overall structure of the text. The third sentence makes a generalization, asserting that evolutionary links between predators and prey can persist across great expanses of time and distance. This generalization is exemplified by the text’s discussion of the relationship between mimosa trees and B. terrenus beetles. When mimosa trees were introduced to South America in 1785, no B. terrenus beetles were present, so the relationship between the trees and the beetles that exists in their native East Africa was disrupted. When the beetles were introduced to South America more than 200 years later, however, they quickly attacked mimosa trees, illustrating the generalization that links between predators and prey "can persist across centuries and continents."

Choice A is incorrect because the third sentence doesn’t indie that Chang and colleagues were investigating any hypothesis. According to the text, Chang and colleagues were simply monitoring mimosa trees when the beetles happened to be introduced to the area. Choice C is incorrect because the third sentence doesn’t discuss any particular species, let alone the species mentioned elsewhere in the text, nor does the sentence explain why species spread to new loions. Choice D is incorrect because the third sentence offers a generalization about the relationship between predators and prey, not an explanation for the findings by Chang and colleagues that’s an "alternative" to an explanation presented elsewhere in the text.