SAT Text Structure and Purpose Question

Adelaide is one of many cities that have installed pontoons or other hardening structures to protect their shorelines against coastal hazards. To assess how birds respond to shoreline hardening and other landscape alterations, Diann Prosser et al. used a tool known as the Index of Waterbird Community Integrity to survey bird communities consisting of sixty-four species, including the tundra swan and the great blue heron, in the Chesapeake Bay on the US East Coast. The researchers concluded that shoreline hardening more negatively affects birds than does land development for uses such as housing. Which choice best describes the overall structure of the text?