Question: In a 3GPP UICC Contact Manager, what is the purpose of the `<UID>` element within the `<3GPPCMGroups>` root element?
Option 1: To store the label of a group for display purposes.
Option 2: To link to a multimedia element associated with a group (e.g., ringtone, voice tag).
Option 3: To contain the unique identifier of a group, matching the X-3GPP-GroupUID in related vCards.
Option 4: To encode the version number of the Groups Definition XML body.
Explanation: The correct answer is Option 3 because the `<UID>` element is specified to contain the unique identifier of a group, which must match the X-3GPP-GroupUID in the vCards belonging to that particular group. This ensures consistency and proper grouping across different elements within the Contact Manager for 3GPP UICC applications.