Question: In a Universal Subscriber Identity Module (USIM) Application Toolkit (USAT), when a Mobile Equipment (ME) encounters a "USSD Return Error", how should it interpret error values not explicitly defined for the Facility (Return Error) information element?
Option 1: The ME shall ignore any undefined error values and only process '00' as a valid response.
Option 2: The ME must query the network for clarification on undefined error values before proceeding.
Option 3: The ME shall interpret all undefined error values as '00', indicating no specific cause can be given.
Option 4: The ME will automatically retry the USSD operation upon receiving an undefined error value.
Explanation: According to USIM Application Toolkit specifications, when encountering a "USSD Return Error", if the error value is not one of the explicitly defined values (with '00' being the only specified value for "No specific cause can be given"), the ME should treat all other values as equivalent to '00'. This ensures consistency in handling unknown error conditions, defaulting to indicating that no specific cause can be provided.