As a network administrator, you issue the interface auto qos voip cisco-phone command on a port in an edge network. It is possible for a Cisco Catalyst switch to check if a Cisco IP Phone is directly attached to that port by:()
A、using DHCP snooping
B、snooping the incoming 802.1Q VLAN tag
C、using CDP
D、snooping the CoS marking on the incoming frames