How does the ERX Edge Router interact with subscriber IP addresses assigned by an external DHCP server?（）

A.It monitors messages from the external server and updates the routing table as needed.
B.It maintains the leases for the DHCP server and reassigns addresses to new subscribers.
C.It sends keep alives to the subscriber and makes the address available when the subscriber stops responding.
D.It sends keep alives to the subscriber and removes the host route when the subscriber stops responding.