正解:A
This is because the arp command is used to display or manipulate the Address Resolution Protocol (ARP) cache, which is a table that maps IP addresses to MAC addresses. The arp command can show the MAC address of a connecting router by using the -a option, which displays the current ARP entries. For example, arp
-a 192.168.1.1 will show the MAC address of the router with the IP address 192.168.1.1. The source of this answer is the Cisco ENCOR v1.1 course, module 3, lesson 3.1: Implementing IPv4 and IPv6 Addressing.