Question: What triggers transitions between the various substates of GMM-REGISTERED?
Option 1: Only cell selection/reselection and change of RA.
Option 2: Cell selection/reselection, change of RA, and loss/regain of coverage.
Option 3: Only loss/regain of coverage and change of RA.
Option 4: None of the above.
Explanation: Transitions between the various substates of GMM-REGISTERED are caused by cell selection/reselection, change of Routing Area (RA), and loss/regain of coverage. This is because these events can affect the MS's ability to access services and maintain its GMM context, leading to changes in the substate.