Company A has deployed a VCS Control and is attempting to register a third-party endpoint. The engineer has confirmed that no traffic is being blocked for the endpoint and it is receiving a valid IP address. Which option could be the cause of this registration failure?

A.	Third-party endpoints are not compatible with VCS Control, only with VCS Expressway.
B.	Cisco Unified Communications Manager is required in addition to the VCS Control.
C.	An incorrect SIP domain is configured on the VCS Control for the endpoint.
D.	The VCS Control must be deployed together with VCS Expressway before endpoints can register to either one.