What is the result of entering the command spanning-tree loopguard default?

A.
The command enables loop guard and root guard.

B.
The command changes the status of loop guard from the default of disabled to enabled.

C.
The command activates loop guard on point-to-multipoint links in the switched network.

D.
The command disables EtherChannel guard.

Explanation:
By default, loop guard is disabled on all switch ports. You can enable loop guard as a global
default, affecting all switch ports, with the following global configuration command:
Switch(config)# spanning-tree loopguard default
You also can enable or disable loop guard on a specific switch port by using the following
interface-configuration command:

Switch(config-if)# [no] spanning-tree guard loop
Although loop guard is configured on a switch port, its corrective blocking action is taken on
a per-VLAN basis. In other words, loop guard doesn’t block the entire port; only the offending
VLANs are blocked. You can enable loop guard on all switch ports, regardless of their
functions. The switch figures out which ports are nondesignated and monitors the BPDU
activity to keep them nondesignated. Nondesignated ports are generally the root port,
alternate root ports, and ports that normally are blocking.
Reference:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuratio
n/guide/stp_enha.html#wp1033825