Final answer:
The correct combination of protocols that adds pruning and grafting to another to create a dynamic multicast shortest path tree is d) PIM-SM, PIM-DM.
Step-by-step explanation:
The question concerns the protocols used in creating efficient and dynamic multicast routing structures within computer networks. Specifically, it asks which combination of protocols adds pruning and grafting to another protocol to create a multicast shortest path tree that can adapt to changes in membership. The correct answer is: d) PIM-SM, PIM-DM. Protocol Independent Multicast-Sparse Mode (PIM-SM) uses a pull model to deliver content only to those routers that have active listeners. PIM-SM starts with a shared tree and can switch to a shortest path tree. Pruning and grafting are mechanisms used in PIM-SM to efficiently manage membership by removing or adding branches of the multicast routing tree. PIM-Dense Mode (PIM-DM), on the other hand, uses a push model initially, flooding the network with multicast traffic and then pruning back branches where there are no listeners. While PIM-DM is not specifically designed to support dynamic membership changes like PIM-SM, the combination of these protocols' mechanisms can create a multicast shortest path tree adaptive to membership changes.