Question: What is a key requirement for Facsimile Group 3 Autocalling/Autoanswering mode in a Public Land Mobile Network (PLMN), especially under certain environmental conditions?
Option 1: Support for simultaneous voice and data transmission
Option 2: Compatibility with only ISDN-connected fax apparatus
Option 3: A high quality of service even under bad radio conditions and/or in connection to/from moving vehicles
Option 4: Mandatory use of the multislot mechanism of GERAN
Explanation: This is correct because maintaining a high quality of service is crucial even when faced with adverse conditions such as poor radio signal strength or when the user equipment (e.g., mobile phone) is in a moving vehicle, ensuring reliable fax transmissions over the PLMN.