What could happen if air pressure is too low in the brake system?

Answer: B — Brakes may not engage at all

If air pressure is too low in the brake system, the brakes may not engage at all. The brake system in a train relies on compressed air to activate the brake cylinders, which apply force to the brake shoes against the wheels. When the air pressure drops below a certain threshold, it can prevent the brake valves from functioning properly, meaning that the brakes cannot be applied as designed. This lack of engagement poses significant safety risks, as it can result in the train being unable to stop when necessary. Therefore, maintaining the correct air pressure is crucial for the effective operation of the train's braking system.