Question: What triggers the inclusion of the 'List of Receive N-PDU Numbers' Information Element in a message?
Option 1: When a UE initiates a new session.
Option 2: Upon receipt of a Routing Area Update Reject message.
Option 3: If the Routing Area Update Accept message contained this IE.
Option 4: During the initial attach procedure.
Explanation: The 'List of Receive N-PDU Numbers' Information Element is included in a message if the Routing Area Update Accept message previously contained this IE, indicating that the network needs to update its records based on the UE's report.