Question: When does the User Equipment (UE) include the non-current native NAS key set identifier IE in an EMM-CONNECTED mode?
Option 1: During every Tracking Area Update Request message.
Option 2: Only when performing a handover from S1 to N1 mode.
Option 3: When the UE has a valid EPS security context and is in idle mode.
Option 4: When the UE performs an A/Gb mode or Iu mode or N1 mode to S1 mode inter-system change and uses a mapped EPS security context.
Explanation: The correct answer requires understanding of specific conditions under which the UE includes the non-current native NAS key set identifier IE. This involves recognizing the importance of inter-system changes (A/Gb, Iu, or N1 to S1 mode) in EMM-CONNECTED mode and the use of a mapped EPS security context for protecting the Tracking Area Update Request message.