问题：

[多选] Which two QoS classification and marking statements are true？ （）

A .  In a Frame Relay network， delay sensitive traffic is tagged with the discard eligible （DE） bit.
B .  In an MPLS network， the three most significant bits of the DSCP or the IP precedence of the IP packet are copied into the MPLS EXP field.
C .  In an MPLS network， the MPLS EXP bits are used to identify up to 16 CoS values.
D .  The differentiated services code point （DSCP） field consists of the first three bits of the IP precedence field in the header of an IP packet.
E .  The 802.1Q standard uses a three bit field referred to as the user priority bits （PRI） to mark packets as belonging to a specific CoS.