Final answer:
The IP address is used for routing because it is globally unique and helps routers determine the source and destination of data packets to facilitate their journey across different networks.
Step-by-step explanation:
The IP address is the one that can be used for routing because it provides global uniqueness. Routing, which is the process by which data packets are forwarded from one network to another, relies on the IP address to determine the source and destination of each packet.
While the MAC address identifies a device on the local network, it does not have the capacity to facilitate routing between different networks. For this reason, routers employ IP addresses to make decisions about where to send packets in order to reach their intended destination on a different network. The IP address structure includes a network part and a host part, which helps in guiding the packet's journey across multiple networks.
Therefore, the correct answer to the question is: a) IP address; it provides global uniqueness.