Which pressure range indicates that a single brake system may require adjustment?

Answer: B — 70-90 psi

The pressure range that indicates a single brake system may require adjustment is 70-90 psi. This range is concerning because it suggests that the brake system may not be functioning optimally. In air brake systems, the ideal operating pressure should typically be above 90 psi for effective braking performance. If the pressure is consistently below this threshold, it could indicate a need for adjustments or maintenance to ensure that the brakes engage properly and safely. Maintaining the correct air pressure in a braking system is crucial for responsiveness and effectiveness. If tire pressure is too low within the specified range, it can affect the system's ability to apply sufficient force and could lead to longer stopping distances or brake failure. Therefore, a pressure reading in this range prompts drivers to assess their braking system to prevent potential safety issues on the road.