Question: What security feature ensures that an intruder cannot determine whether different services are delivered to the same user by eavesdropping on the radio access link?
Option 1: User Identity Confidentiality
Option 2: User Location Confidentiality
Option 3: Ciphering of Signalling and User Data
Option 4: User Untraceability
Explanation: User untraceability is a security feature that ensures an intruder cannot deduce whether different services are delivered to the same user by eavesdropping on the radio access link. This feature is essential in maintaining the confidentiality of user identity and preventing unauthorized tracking of users' activities.