Concept:Soil erosion is the removal of the fertile top layer of soil by agents such as wind and water.
Human activities that expose soil to these agents increase the risk of erosion.
Explanation:Bush burning destroys vegetation cover, leaving the soil bare and prone to erosion.
Overgrazing removes grass and compacts the soil, increasing erosion.
Excavation disturbs the land surface, creating loose soil that can be easily carried away.
Reafforestation, however, involves planting trees, which protects the soil and reduces erosion.
Thus, the possible causes are i, ii and iv only.
Answer:A. i, ii and iv only