Question: What is the primary purpose of the `<passwd>` field in the `+CLCK` action command syntax, specifically when dealing with the "FD" facility (SIM card or active application in the UICC fixed dialling memory feature)?
Option 1: To authenticate the User Equipment (UE) to the network for voice calls.
Option 2: To unlock the SIM/UICC card installed in the currently selected card slot.
Option 3: To authorize access to supplementary services not related to fixed dialling.
Option 4: To provide PIN2 authentication, required if not done during the current session, for accessing the fixed dialling memory feature.
Explanation: The correct answer is Option 4 because, when dealing with the "FD" facility (fixed dialling memory feature of the SIM card or an active UICC application), if PIN2 authentication has not been performed during the current session, the `<passwd>` field must provide the PIN2 to access this feature, ensuring an additional layer of security for accessing and managing the fixed dialling numbers stored in the SIM/UICC.