When would you require a voice gateway?

You are CCNA VOICE associate in Certkey.com. When would you require a voice gateway? (Choose two.)

A.
When you connect a branch location to IP WAN

B.
When you connect a branch location using VoIP to the PSTN

C.
When you connect a Cisco Unified Communications Manager to a LAN

D.
When you connect a Cisco Unified Communications network to a PBX