A user is dialing an external PSTN number with a prefix of 01 from a Cisco TelePresence SX10 Quick Set in a Cisco VCS environment. In the past, the Cisco VCS and the ISDN gateway were correctly configured with a prefix of 01, but the calls are now failing. What are three possible causes?

A.	The Cisco VCS Control is down.
B.	The interworking setting is turned off.
C.	The audio feature in the Cisco TelePresenceSX10 is turned off.
D.	The SIP trunk is not configured on the gateway.
E.	01 is not a valid prefix.
F.	ISDN is not enabled on the Cisco TelePresenceSX10.
G.	The Cisco TelePresenceSX10 is not registered to the Cisco VCS Control.
H.	The Cisco TelePresenceSX10 is not registered to the Cisco Express C.