Question: In which mode must the UE be in order to use the transport of NAS messages procedure for carrying SMS messages between the MME and the UE?
Option 1: EMM-IDLE mode
Option 2: EMM-CONNECTED mode
Option 3: EMM-DEREGISTERED mode
Option 4: EMM-AUTHENTICATED mode
Explanation: The transport of NAS messages procedure can only be used when the UE is in EMM-CONNECTED mode, as specified in the 3GPP TS 24.301 document. This ensures that the UE has an established connection with the network and can exchange NAS messages for SMS transmission.