Question: Upon receiving SIB7, what action(s) does a User Equipment (UE) take if the received `messageIdentifier` or `serialNumber`, or both, are different from the current values for SIB7?
Option 1: Use the new values, discard previously buffered segments, and continue receiving SIB7 until all segments of the warning message are gathered.
Option 2: Immediately forward the received segment to upper layers without waiting for all segments of the warning message.
Option 3: Discard the current and newly received `messageIdentifier` and `serialNumber` values, then stop SIB7 reception.
Option 4: Store the new segment but do not update the current `messageIdentifier` and `serialNumber` values until all segments are received.
Explanation: According to the specified behavior for handling SIB7, if the UE receives a `messageIdentifier` or `serialNumber`, or both, that differ from the current values, it should update these values (using the received ones), discard any previously stored warning message segments (to avoid mixing segments of different messages), and then continue receiving SIB7. Once all segments of the new warning message are received, it assembles the message and forwards it to upper layers, after which it stops SIB7 reception and discards the current `messageIdentifier` and `serialNumber` values. This ensures the UE processes the latest warning message correctly.