What functionality hangs up on a remote caller and looks at a table of predefined phone numbers?

A.
Caller ID

B.
RAS

C.
Callback

D.
NOS

Explanation:
The goal of a callback system is to provide another layer of
authentication. For an attacker to successfully compromise this setup and obtain
unauthorized access she would need to be at the predefined phone number or
reconfigure the telephone companys equipment to forward the call on to her.