Question: What triggers the transition to the GMM-DEREGISTERED state when a Mobile Station (MS) is attached for emergency bearer services?
Option 1: The MS switches from PMM-CONNECTED mode to PMM-IDLE mode.
Option 2: The periodic routing area update timer expires while the MS is in PMM-IDLE mode.
Option 3: A GPRS detach or combined GPRS detach procedure is performed.
Option 4: The MS loses coverage and then regains it.
Explanation: According to the provided text, when an MS attached for emergency bearer services is in PMM-IDLE mode and its periodic routing area update timer expires, the state GMM-DEREGISTERED is entered. This specific scenario highlights a condition that triggers the transition to the GMM-DEREGISTERED state, focusing on the behavior of the MS in relation to emergency bearer services and periodic updates.