Question: What is the condition for retaining the current KgNB during an intra-gNB-CU handover, as indicated by the gNB in the HO Command message?
Option 1: The current KgNB can always be retained.
Option 2: The current KgNB can only be retained if an unused {NH, NCC} pair is available in the gNB.
Option 3: The current KgNB can only be retained if no unused {NH, NCC} pair is available in the gNB.
Option 4: The current KgNB cannot be retained during intra-gNB-CU handover.
Explanation: According to the 3GPP specification, retaining the current KgNB shall only be done during intra-gNB-CU handover if an unused {NH, NCC} pair is available in the gNB. This ensures secure key management and prevents potential security breaches.