Hydraulic brakes or air brakes should not be fanned except...?

Answer: A — On slippery pavement

Fanning hydraulic or air brakes in any scenario is not recommended, as it can cause excessive wear and damage to the braking system. However, if it is absolutely necessary to fan the brakes, it should only be done on slippery pavement to avoid locking the wheels and losing control of the vehicle. Fanning the brakes during regular stops or when the bus is fully loaded can cause uneven wear on the brakes and decrease their effectiveness. Fanning brakes at high speeds can also be dangerous as it can overheat the brakes and reduce their stopping power.