Question: In Mobile Radio Interface Layer 3, what does the `areaList` identifier primarily refer to for a Mobile Station (MS)?
Option 1: A single geographic location for emergency service purposes.
Option 2: A set of one or more areas for voice call routing optimization.
Option 3: Parameters defining a cell's coverage area for handover decisions.
Option 4: A set of one or more areas for periodic and triggered area event reporting.
Explanation: The correct answer, Option 4, aligns with the specification that the `areaList` identifier is used to denote a collection of areas. This is crucial for Location Services (LCS) in mobile networks, where periodic and triggered reporting helps in tracking the location of the MS within these defined areas, facilitating services like location-based services or emergency calls. The other options are incorrect as they do not accurately describe the purpose of `areaList` in the context of supplementary services for mobile radio interface layer 3.