The suggested answer is A, C.
If a host remains stuck in the Registration VLAN during the on-boarding process, two possible reasons are: the wrong agent installed on the host or another unregistered host present on the same port. The wrong agent might not allow proper communication with the system, preventing the host from being properly registered and moved out of the Registration VLAN. Additionally, if there is another unregistered host on the same port, it could cause network conflicts that prevent the registered host from transitioning to the appropriate VLAN.