On which types of network will OSPF elect a backup designated router?（）

A.to prevent unauthorized Telnet access to a switch port
B.to limit the number of Layer 2 broadcasts on a particular switch port
C.to prevent unauthorized hosts from accessing the LAN
D.to protect the IP and MAC address of the switch and associated ports
E.to block unauthorized access to the switch management interfaces over common TCP ports

A.permit all packets matching the first three octets of the source address to all destinations
B.permit all packets matching the last octet of the destination address and accept all source addresses
C.permit all packets from the third subnet of the network address to all destinations
D.permit all packets matching the host bits in the source address to all destinations
E.permit all packets to destinations matching the first three octets in the destination address

A.Establish a direct link from the switch to all other switches in the network.
B.Assign the switch a higher MAC address than the other switches in the network have.
C.Configure the switch so that it has a lower priority than other switches in the network.
D.Configure the switch for full-duplex operation and configure the other switches for half-duplex operation.
E.Connect the switch directly to the MDF router， which will force the switch to assume the role of root bridge.