Concept:The Sudan savanna is a major crop-producing zone in Nigeria.Explanation:Millet, sorghum, maize, and onions thrive in the Sudan savanna.This zone has moderate rainfall and fertile soil that support these crops.The Sahel savanna is too dry for maize and onions.The tropical rainforest and montane forests have different climate conditions.Therefore, the Sudan savanna is the correct vegetation zone.Answer:B. Sudan savanna.