A.Classifying and marking traffic should be done as close to the traffic source as possible. 
B.Classifying and marking traffic should be done at the distribution layer.
C.Traffic is classified and marked as it travels through the network.
D.If untrusted traffic enters a switch， it can be marked with a new QoS value appropriate for the policy in place.
E.The trust boundary moves depending on the type of traffic entering the network.