802.1X authentication on a network switch like SW2 involves different modes of access control, primarily MAC address-based and interface-based. In the MAC address-based mode, each client (like 802.1X Clients A and B) needs to be authenticated separately based on their MAC addresses. In the interface-based mode, once any client (e.g., Client A) connected to that interface is authenticated, other clients (e.g., Client B) can also access the network via the same interface. Therefore, A is correct because each client must be authenticated separately in MAC address-based control. B is also correct as in interface-based control, once one client is authenticated, other clients connected to the same interface can access the network without separate authentication. Option C is incorrect because in MAC address-based mode, if Client A (who authenticated first) goes offline, the status of the interface does not allow Client B to maintain network access automatically since each client needs separate authentication. Option D is incorrect because in the interface-based control mode, if Client A goes offline, it does not necessarily cause Client B to lose network access permissions immediately.