One way to limit connections to a system is by calling back the number of a previously authorized location. This type of access protection system is called a:

A.
Sendback system

B.
Callback forward system

C.
Callback system

D.
Sendback forward system

Explanation:
Callback systems provide access protection by calling back the number
of a previously authorized location. This control can be compromised by call
forwarding, however.