Which action is a direct cause of desertification?
(1) contaminating fresh water supplies
(2) burning fossil fuels in factories
(3) damming rivers to produce hydroelectricity
(4) removing vegetation through overgrazing

The best anwer is 4); vegetation is vital from keeping a place from becoming a desert. It transforms the ground into that with more nutrients, captures water and stops erosion, as well as protects the nutrient parts of the soil from being carried away with the wind.