Which geographic factors contributed to the decline of Sumer? Choose all answers that are correct. A. Irrigation of the crops led to salinization of the soil. B. Sumer was located on a flat plain that provided no natural barriers to invasion. C. Mountains made agriculture difficult. D. The land became too swampy to grow adequate crops.
It's A Irrigation was overused, the soil didn't get any rest (crop rotation is a younger invention), the result was salinization of the soil, which led to decline of Sumer.
