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Question 99·Hard·Command of Evidence

Using stable isotope analysis of preserved barley grains from Archaic-period settlements along the lower Indus River, archaeobotanist Leena Patel and colleagues found unexpectedly low 13 ⁣C/12 ⁣C^{13}\!C/^{12}\!C ratios—values that typically indicate crops experienced little water stress. Because paleoclimate data show limited rainfall in the region around 4000 BCE, Patel’s team argues that local farmers must have practiced organized flood irrigation centuries earlier than previously documented.

Which finding, if true, would most directly support Patel’s conclusion?