Before driving a vehicle with a dual air system, the air compressor must build up to a minimum of how many psi on both the primary and secondary systems?

Answer: B — 100 psi

In a dual air system, two independent brake circuits power the vehicle—the primary for normal braking and the secondary for emergency/parking braking. Before moving, both circuits must reach at least 100 psi. This gives you enough stored air to maintain braking reliability and to safely release or engage the parking brakes if one circuit starts to drop pressure. Driving at lower pressures could leave you with insufficient air if there’s a leak or heavy brake use, risking brake failure or inability to release the parking brakes. The required minimums are 100 psi on each circuit, not the other values listed.