Question: What is the primary purpose of setting the `CS-Service-QoS-Request-Operation` AVP to `MODIFICATION (1)` in a Policy and Charging Control (PCC) context?
Option 1: To notify the network that a User Equipment (UE) has changed its location.
Option 2: To request additional resources for a new IP flow without altering existing QoS settings.
Option 3: To inform the PCC rule function about a change in the UE's subscription profile.
Option 4: To modify the reserved resources associated with specific QoS request identifiers for a CS service.
Explanation: In the context of Policy and Charging Control (PCC), setting the `CS-Service-QoS-Request-Operation` AVP to `MODIFICATION (1)` signals a request to adjust or update resources allocated for certain QoS requirements, identified by their QoS request identifiers, to meet altered service needs.