After you define the open logical channel on a private network terminal inside a firewall, if (), the media streams can be transmitted in one direction only.

After you define the open logical channel on a private network terminal inside a firewall, if (), the media streams can be transmitted in one direction only.
A . The firewall does not have the relevant port enabled.
B . The private IP address cannot be found for media stream transmission.
C . The master and slave relationship cannot be determined.
D . Capability negotiation cannot be implemented.

Answer: A