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
