Link state routing is a type of routing protocol that is used to determine the best path for data packets to travel through a network. It is based on the concept of each router having a complete map of the network, including the status and cost of each link. This allows the routers to make informed decisions about the best path to forward packets.

The correct answer to the question is option 'B', which states that OSPF (Open Shortest Path First) uses link state routing. OSPF is a widely used routing protocol that is used in IP networks, particularly in large enterprise networks. It is designed to be scalable and efficient, and it uses link state routing to determine the shortest path between routers.

Here is a detailed explanation of why OSPF uses link state routing:

1. Link State Database:
- In OSPF, each router maintains a Link State Database (LSDB) that contains information about the network topology.
- The LSDB is built by exchanging Link State Advertisements (LSAs) between routers.
- LSAs contain information about the router's neighbors, the links it is connected to, and the cost of those links.
- By exchanging LSAs, routers can build a complete map of the network and have the same information about the network topology.

2. SPF Algorithm:
- OSPF uses a Shortest Path First (SPF) algorithm to calculate the best path for packets to travel.
- The SPF algorithm takes into account the cost of each link, which is determined by the administrator.
- It calculates the shortest path by summing up the costs of the links along a path.
- The path with the lowest total cost is considered the best path, and packets are forwarded along that path.

3. Dynamic Updates:
- OSPF supports dynamic updates, which means that routers can exchange LSAs to keep the LSDB up to date.
- When a link goes down or a new link is added to the network, routers exchange LSAs to inform each other about the changes.
- This allows OSPF to adapt to changes in the network and recalculate the best path if necessary.

In conclusion, OSPF is an example of a routing protocol that uses link state routing. It maintains a Link State Database and uses the SPF algorithm to calculate the best path for packets to travel through the network. OSPF is widely used in large networks because of its scalability and efficiency.