Final answer:
A combination vehicle air brake system cannot leak more than 3 psi per minute with the engine off and brakes 'released'.
Step-by-step explanation:
The question pertains to the standards for air leak rates in combination vehicle air brake systems. According to the Federal Motor Carrier Safety Regulations, a combination vehicle air brake system cannot leak more than 3 psi per minute with the engine off and brakes 'released'. This is a vital safety measure to ensure that the air brake system maintains its integrity and provides reliable braking performance.