SAT Text Structure and Purpose Question

In Bhutan, use of solid fuel (e.g., coal wood) as a share of total household fuel use fell by approximately two thirds between 2000 and 2019; such shifts are often explained by appeal to the energy ladder, a model holding that fuel choice is mediated mainly by household income (specifically, high technology fuels displace solid fuels as incomes rise). Rasmus Heltberg's study of fuel use in Nepal shows this model to be reductive, however; household fuel use was heterogeneous, flexible, and influenced by several factors, including the stability of the local electrical grid. Which choice best describes the main purpose of the text?