Question: What is the primary purpose of the EFGID1 (Group Identifier Level 1) file in a Universal Subscriber Identity Module (USIM) application, as indicated by its presence when service n° 17 is "available"?
Option 1: To store individual subscriber authentication keys for secure network access.
Option 2: To identify a group of USIMs for a particular application or service.
Option 3: To manage the prioritization of services (e.g., voice over data) on the User Equipment (UE).
Option 4: To log historical network usage patterns for billing purposes.
Explanation: The correct answer, Option 2, reflects the EFGID1's role in identifying a group of USIMs tailored for a specific application, as directly inferred from the provided context. This highlights its utility in service provisioning and management at a group level rather than individual subscriber security (Option 1), service prioritization (Option 3), or usage logging (Option 4).