Final answer:
During an air brake pre-trip inspection on a vehicle with one trailer, you should make sure that air loss is not more than 2 p.s.i. within one minute.
Step-by-step explanation:
During an air brake pre-trip inspection on a vehicle with one trailer, you should make sure that air loss is not more than 2 p.s.i. within one minute. This is important to ensure that the air brakes are working properly and that the pressure remains at a safe level for effective braking. If there is more than 2 p.s.i. of air loss within one minute, it could indicate a problem with the brakes and they should be addressed before driving the vehicle.