How many messages does Internet Key Exchange use to negotiate SA characteristic when it runs inaggressive mode？（）

A.SNMP version 2 uses a proxy agent to forward GetNext message to SNMP version 3.
B.SNMP version 2 supports message integrity to ensure that a packet has not been tampered with
C.Proxy agents were used only in SNMP version 1.
D.SNMP version 3 supports encryption and SNMP version 2 support authentication.
E.GetBulk messages are converted to GetNext messages by the proxy agent and are then forwarded to the SNMP version 1 agent.

A.Default MDT groups are used for PIM control traffic， low-bandwidth sources， and flooding of sparse mode traffic.
B.MDTs are built in customer networks
C.Data MDT groups are used for high-bandwidth sources to reduce replication to uninterested PEs.
D.MDTs are built in provider networks
E.The number of MDTs depends on PIM modes of MDT groups.

A.AAL2
B.AAL 4
C.AL 5
D.AAL 1
E.AAL 3