Which statement about SS& message routing and addressing methods is true?

A.
The SGSN does not know the subscriber IMSI

B.
Messages can be addressed in two ways: by IMSI and by GTT

C.
All configuration areas are required, especially if the routing is based purely on
DPC+SSN

D.
There are three ways to address an SS7 message: by IMSI, by GTT and by DPC + SSN

Explanation: