A.Administratively shut down the interfaces.
B.Physically secure the interfaces.
C.Configure a virtual terminal password and login process.
D.Enter an access list and apply it to the terminal interfaces using the access-class command.
E.Create an access list and apply it to the terminal interfaces using the access-group command.

A.DLCI 17 describes the ISDN circuit between R2 and R3.
B.DLCI 17 describes a PVC on R2. It cannot be used on R3 or R1.
C.DLCI 17 is the Layer 2 address used by R2 to describe a PVC to R3.
D.DLCI 17 describes the dial-up circuit from R2 and R3 to the service provider.