Refer to the exhibit.  Which three statements are true about trust boundaries in the campus  network？（）

• A、Classification and markingoccur using 802.1ab QoS bits before reaching the trust boundary.  
• B、A device is trusted if it correctly declassifies packets. 
• C、A device is trusted if it correctly classifies packets.
• D、Network trust boundaries are automatically configured in IOS version 12.3 and later.  
• E、The outermost trusted devices represent the trust boundary.
• F、For scalability， classification should be done as close to the edge as possible.