Question: What is the primary purpose of the Nnef_ApplyPolicy_Update service operation in the 5G System?
Option 1: To update a policy to the UE.
Option 2: To negotiate a new background data transfer policy.
Option 3: To retrieve the result of a previous policy update.
Option 4: To cancel an ongoing policy application.
Explanation: The Nnef_ApplyPolicy_Update service operation is used by the consumer to request an update to a policy on the UE. This is evident from the description and inputs required for this service operation, which include the Transaction Reference ID and Background Data Transfer Reference ID for a previously negotiated policy.