Concept:The Nupe people are well known for their traditional craft specialisation, particularly in leather goods.
Explanation:The Nupe of central Nigeria are famous for producing fine leather items such as bags, sandals, and cushions.
They are also noted for glass beads, brass trays, and woven mats, but leather work stands out as their key economic craft.
Among the listed options, gathering, hunting, and cattle rearing are not the characteristic main activity of the Nupe.
Therefore, the main economic activity of the Nupe people is leather work.
Answer:A. leather work