Question: Where will a capability related to a feature that can be used in both S1 mode and at least one of A/Gb or Iu modes, but is only used by the MME, be signalled?
Option 1: In the MS network capability IE
Option 2: In the UE network capability IE for S1 mode only
Option 3: In both MS network capability IE and UE network capability IE
Option 4: In the UE network capability IE
Explanation: According to the guidelines, if a capability is related to a feature that can be used in both S1 mode and at least one of A/Gb or Iu modes, but is only used by the MME, it will be signalled in the UE network capability IE. This ensures that the information is available to the MME for its operations.