What must you remember when you want to use the ramp or lift of a bus?

You answered correctly. According to German traffic rules, the ramp or lift on a bus must only be operated when the bus is completely stationary. This ensures safety for passengers entering or exiting the bus and prevents accidents or damage to the equipment. Moving the ramp or lift while the bus is in motion is not allowed because it could cause injury or mechanical failure. Remembering this rule helps maintain safe boarding and alighting procedures on buses.