Question: What action does the VLR/SGSN take when it receives a synchronization failure message from the user?
Option 1: It sends a new user authentication request to the user.
Option 2: It ignores the message and continues with the existing authentication process.
Option 3: It sends an authentication data request with a "synchronization failure indication" to the HE/AuC.
Option 4: It deletes the old authentication vectors for that user in the VLR/SGSN.
Explanation: When the VLR/SGSN receives a synchronization failure message from the user, it sends an authentication data request with a "synchronization failure indication" to the HE/AuC, along with specific parameters. This is done to initiate the re-synchronization procedure and ensure that the authentication process can continue successfully.