If the secondary service circuit fails, which brakes will cease to function?

Answer: B — Steering axle brakes

When the secondary service circuit fails, the brakes that will cease to function are the steering axle brakes. In a typical air brake system, the steering axle brakes are often part of the primary function of the braking system designed to ensure maximum control and maneuverability of the vehicle. The primary service circuit is responsible for these crucial brakes, allowing them to operate effectively during normal driving conditions. If there is a failure in the secondary service circuit, which is usually associated with additional braking functions or redundancies that may support the trailer or rear axle, the steering axle brakes can be impacted. Thus, the correct understanding is that the steering axle brakes are integral to the primary braking mechanism and would face issues if the secondary system does not perform, leading to a potentially compromised driving situation.