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Question 120·Hard·Text Structure and Purpose

Urban ecologist Leena Dhar led a study tracking temperatures at 40 bus shelters across Phoenix during a three-week heatwave. Her team installed "living roofs"—shallow trays of native succulents—on half the shelters and left the others unchanged, then monitored shaded air temperature and surface heat. The modified shelters consistently recorded lower surface temperatures and slightly cooler shaded air, and riders reported feeling "less baked" while waiting. City staff, however, note that irrigation upkeep could be costly and uneven across neighborhoods, so the department has requested a cost–benefit analysis before considering a citywide rollout.

Which choice best describes the overall structure of the text?