The DD (Database Description) message in the OSPF protocol has ______.(Multiple choice)

The DD (Database Description) message in the OSPF protocol has ______.(Multiple choice)
A . Negotiate the master-slave relationship of interaction
B. Describe the summary information of the LSA
C. Respond to the LSA message and send the complete LSA requested by the neighbor router
D. When the router is in the ExStart state, maintain the neighbor relationship

Answer: AB