Concept:Cattle ranching in West Africa depends on environmental conditions that allow cattle to survive and remain healthy.Explanation:The forest region of West Africa is not suitable for cattle ranching mainly because the tsetse fly is common there.The tsetse fly transmits trypanosomiasis, a disease that is harmful to cattle.This disease weakens and kills cattle, making large-scale ranching difficult in the forest zone.Scarcity of grass is not the main reason because the forest has undergrowth, but the tsetse fly remains the key limiting factor.Answer:B. Presence of tsetse flies