What was the most important factor in making mesopotamia's farmland fertile?

Item 14 which statement is an accurate description of the transatlantic slave trade? africans were brought to the americas in a three-part system of triangular trade. slaves went from europe to africa, and then to the americas in a circle of trade. native american slaves were sent to europe in exchange for sugar and molasses. africans traded tobacco and furs for captured arabs whom they sold into slavery.