Final answer:
The Address Resolution Protocol (ARP) is used to associate MAC addresses with IP addresses, enabling communication on a local network.
Step-by-step explanation:
ARP (Address Resolution Protocol) is used to associate MAC addresses and IP addresses. Therefore, the correct option is: a. MAC addresses, IP addresses. ARP plays a crucial role in local network communication by mapping IP addresses to corresponding MAC addresses. When a device on a local network needs to communicate with another device, it uses ARP to discover the MAC address associated with a specific IP address. This mapping is essential for the proper functioning of Ethernet networks, allowing devices to correctly address and deliver network packets based on the hardware MAC addresses while utilizing IP addresses for higher-level routing and logical network organization. Options b, c, and d involve different network protocols and identifiers not directly associated with ARP's primary purpose.