What does the redundant interface feature of the security appliance accomplish?

What does the redundant interface feature of the security appliance accomplish?

A.
to increase the number of interfaces available to your network without requiring you to add additional physical interfaces or security appliances

B.
to increase the reliability of your security appliance

C.
to allow a VPN client to sendIPsec-protected traffic to another VPN user by allowing such traffic in and out of the same interface

D.
to facilitate out-of-band management