In the scenario where a private network terminal calls a public network terminal, when the logical channel is opened, the media stream will be unidirectional. The reason may be which of the following?

In the scenario where a private network terminal calls a public network terminal, when the logical channel is opened, the media stream will be unidirectional. The reason may be which of the following?
A . The firewall does not open the corresponding port.
B . The public network terminal cannot find the private network address.
C . The terminal cannot perform master-slave determination.
D . The terminal cannot perform capability negotiation.

Answer: A