Under normal conditions, in order to engage the parking brakes, the driver must first:
A. Turn off the engine.
B. Let the air out of the air brake system.
C. Be sure that the air brake system is fully pressurized.
Answer: B. Let the air out of the air brake system.
If the answers is incorrect or not given, you can answer the above question in the comment box. If the answers is incorrect or not given, you can answer the above question in the comment box.