What should the administrator investigate?

Refer to the exhibit.

The exhibit shows configurations for interface 5 and VLAN 20. Note that DHCP snooping and ARP protection are also enabled.

A network administrator finds that interface 5 on an AOS-Switch is disabled. The administrator re-enables the interface, but it shuts down again.

What should the administrator investigate?
A . a device that sends too much unicast traffic
B . rogue DHCP server
C . a loop on the interface
D . a device that sends unauthorized ARP messages

Answer: C