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 802.10 standard uses a three bitfield referred to as the user priority bits （PRI） to mark packets as belonging to a specific CoS.