Final answer:
When the brakes are applied and the engine is off, air loss in a straight truck or bus's brake system should not exceed 2 psi in one minute to ensure safe operation.
Step-by-step explanation:
The question at hand pertains to the acceptable air loss in a straight truck or bus's air brake system when the brakes are applied and the engine is turned off. According to safety standards, the air loss should not be excessive to ensure the vehicle can be safely operated and parked.
Therefore, the correct answer to the question 'With brakes applied and engine off, air loss in a straight truck or bus should not exceed?' is 2 psi in one minute. This is an important safety check to ensure the vehicle's brake system is operating correctly and will be able to perform in a critical situation to prevent accidents.
When the brakes are applied and the engine is off, the air loss in a straight truck or bus should not exceed 3 psi in one minute. This is because the air pressure in the braking system should remain relatively stable for a short period of time.