A.Endpoints 2 and 3 are optimal places to establish a trust boundary. Endpoint 1 is an acceptable  place to establish a trust boundary.
B.Endpoint 2 is the optimal place to establish a trust boundary. Endpoints 1 and 3 are acceptable  places to establish a trust boundary.
C.Endpoint 2 is the only acceptable place to establish a trust boundary.  
D.Endpoint 1 is the only acceptable place to establish a trust boundary.
E.Endpoints 1 and 2 are optimal places to establish a trust boundary. Endpoint 3 is an acceptable  place to establish a trust boundary.
F.Endpoint 1 is the optimal place to establish a trust boundary. Endpoints 2 and 3 are acceptable  places to establish a trust boundary.

A.The default CoS value for incoming traffic is set up to 0.
B.The CoS value is trusted for 802.1p or 802.1q tagged traffic.
C.PortFast is automatically disabled when a voice VLAN is configured.
D.The voice VLAN feature is disabled by default.
E.The IP phone accepts the priority of all tagged and untagged traffic and sets the CoS value to 4.
F.When the voice VLAN feature is enabled， all untagged traffic is sent according to the default  CoS priority of the port