Which of the following vegetation zones is found immediately south of the Sahara Desert in West Africa?

The Sahel savanna is the transitional zone located immediately south of the Sahara Desert, characterised by sparse, drought-resistant grasses and shrubs receiving about 250–500 mm of rainfall annually. It acts as a buffer between the desert and the wetter Sudan savanna further south. The Sudan savanna lies south of the Sahel, while derived savanna results from human degradation of forest.