Through which two procedures does a direct tunnel session change to a two-tunnel session? (Choose two.)
A. Iu-release request procedure initiated by RNC
B. GTPU-error indication by the RNC to the GGSN
C. UE-initiated secondary PDP context activation
D. successful GGSN-initiated PDP modification procedure
E. successful UE-initiated PDP modification procedure
F. periodic RAU procedure triggered by the UE
