Which of these is disadvantage of single-zone (VCS) WAN model?

A.
No endpoints will be able to place calls if connectivity is lost to the VCS location.

B.
Not all signaling goes through the VCS in the headquarters, causing signaling traffic
across the WAN link.

C.
If interworking required, the media does not go through the VCS in the headquarters,
even if the video call is local from a branch office endpoint to another endpoint that office.

D.
Flexibility cannot be assured in the headquarters configuration.