Final answer:
The medium used in the Throne of King Nsa'ngu includes wood, glass beads, and cowrie shells.
Step-by-step explanation:
The medium used in the Throne of King Nsa'ngu is all of the above: wood, glass beads, and cowrie shells. This can be inferred from the detailed representations in historical artifacts and the use of these materials in various cultural items, as described in the reference information. Cowrie shells were notably used for internal trade and therefore had a significant value and symbolic meaning in the context of the region, which adds cultural significance to their use in an object as important as a king's throne. Similarly, glass beads and wood were commonly used materials in African art forms and cultural artifacts.