Question: What triggers the UE to enter the EMM-REGISTERED state?
Option 1: When the detach procedure is performed by the UE.
Option 2: When the attach or combined attach procedure is performed by the UE.
Option 3: When the UE receives a paging message from the network.
Option 4: When the UE performs a tracking area update procedure.
Explanation: The EMM-REGISTERED state is entered at the UE when it successfully completes an attach or combined attach procedure, indicating that the UE has registered with the network and is now in a registered state.