Question: What is primarily represented by the `CSService` class in the context of Telecommunication Management's Subscription Management (SuM) Network Resource Model (NRM)?
Option 1: A Packet Switched (PS) service provided to a subscriber.
Option 2: A set of attributes defining a network resource from a provider perspective.
Option 3: A Circuit Switched (CS) service offered by a service provider, encompassing valid subscription parameters.
Option 4: An integration reference point for information services between different networks.
Explanation: The `CSService` class specifically represents a Circuit Switched (CS) service, containing valid parameters defining this CS service from a subscription viewpoint, aligning with how CS services are managed and provided by telecom service providers.