Question: What should a mobile station do if it receives a RECALL message but does not support the "Network initiated MO call" option?
Option 1: Ignore the message and continue with current activities.
Option 2: Send an error message to the network indicating that the option is not supported.
Option 3: Treat the message as a message with message type not defined for the PD.
Option 4: Automatically initiate the sending of the SETUP message.
Explanation: According to the specification, if a mobile station does not support the "Network initiated MO call" option, it should treat the RECALL message as a message with message type not defined for the PD. This ensures that the mobile station handles the message correctly and avoids any potential errors or misinterpretations.