Which two statements are true about trust boundaries？（）

• 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.