Which top-level IOS command is needed to begin the configuration of a Cisco Unified Communications Manager Express gateway to enable phones to be registered via SIP? 

Answer options:

A. allow-connections sip to sip
B. voice service voip
C. voice register global
D. voice register dn

C

Reference: https://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-manager-express/99946-cme-sip-guide.html