Refer to the graphic.
VLANs 10 and 20 have been created on both SWA and SWC. VLAN 10 has been manually created on SWB. SWB has learned VLAN 20 from SWA via GVRP, allowing the hosts to belong to different VLANs as shown. If port Interface G0/0/1 on SWB is changed to fixed mode, what will happen?
If the port Interface G0/0/1 on SWB is changed to fixed mode, it will only transmit the manually configured VLANs and will no longer dynamically register VLANs through GVRP. Since VLAN 10 is manually created on SWB, Hosts A and C, which belong to VLAN 10, will still be able to communicate. However, Host B and Host D, which belong to VLAN 20, will not be able to communicate because VLAN 20 was learned dynamically and won't be transmitted in fixed mode. Therefore, hosts that belong to the same VLAN (VLAN 10) will still be able to communicate, but VLAN 20 hosts will not.
Fixed: In this mode, the GVRP interface is disabled from dynamically registering and deregistering VLANs and can only transmit the static VLAN registration information. If the registration mode is set to fixed for a trunk interface, the interface allows only the manually configured VLANs to pass, even if the interface is configured to allow all the VLANs to pass.
If A is right answer than why not B
SW B doesnt have vlan 20