Which choice best describes the function of the underlined portion in the text as a whole? Industrial activity is often assumed to be a threat to wildlife, but that isn't always so. Consider the silver-studded blue butterfly (Plebejus argus): as forest growth has reduced grasslands in northern Germany, many of these butterflies have left meadow habitats and are now thriving in active limestone quarries. In a survey of multiple active quarries and patches of maintained grassland, an ecologist found silver-studded blue butterflies in 100% of the quarries but only 57% of the grassland patches. Moreover, butterfly populations in the quarries were four times larger than those in the meadows.

Choice B is the best answer because it most accurately describes how the underlined portion functions in the text as a whole. The first sentence presents the general claim that industrial activity is not always a threat to wildlife. The underlined portion of the sentence that follows suggests that the silver-studded blue butterfly is an example of wildlife thriving in areas of industrial activity: active limestone quarries. Thus, the function of the underlined portion is to introduce a specific example in support of the general claim in the previous sentence. Choice A is incorrect. Although the first sentence indicates that 'industrial activity is often assumed' to harm wildlife, in the case of the silver-studded blue butterfly the text mentions neither an assumption about this species nor any challenge to such an assumption. Choice C is incorrect because the text mentions only one study: the 'survey.' Additional studies are not mentioned in the text. Choice D is incorrect because neither the underlined portion nor any other portion of the text provides a definition for any of the terms used in the text's argument.