What action must not be taken by passengers while on a moving SPAB?

Passengers must not stand up while the SPAB is in motion primarily due to safety concerns. Standing while the bus is moving increases the risk of falls and injuries, as the vehicle can make sudden stops or turns. Safety regulations mandate that all passengers remain seated with their seatbelts fastened to ensure their protection during transit.

The other options involve behavior that is acceptable and often necessary for safety and communication. For instance, talking to the driver can be appropriate in case of emergencies or to provide important information, as long as it is done without distraction. Additionally, passengers are required to fasten their seatbelts and to follow the driver's directions to maintain order and safety on the bus. Thus, remaining seated is the key action that must not be violated while the SPAB is moving.