What is the warning air pressure level in the service air tank that a driver needs to watch for?

Answer: B — 60 psi

The warning air pressure level in the service air tank that drivers need to monitor is indeed 60 psi. This is an important threshold because it signals to the driver that the air pressure has dropped to a point where the braking system may not function effectively. When the pressure falls to this level, a warning light or buzzer will typically activate, alerting the driver to take action, such as ensuring there is enough air pressure before continuing driving or safely stopping the vehicle to address the issue. In commercial vehicles, maintaining the correct air pressure is crucial for safe braking, and understanding this warning level is part of responsible vehicle operation to prevent accidents due to brake failure.