[单项选择题] Old SGSN can get new SGSN’s IP address by communicating to （） when a MS requests inter_SGSN

[单项选择题] Old SGSN can get new SGSN’s IP address by communicating to （） when a MS requests inter_SGSN RA update.

A.MS

B.GGSN

C.DNS

D.HLR