After connecting the airlines, but before backing under the trailer, you should:
A. Supply air to the trailer system, then pull out the supply knob.
B. Make sure that the trailer brakes are off.
C. Walk around the rig to be sure it is clear.
Answer: A. Supply air to the trailer system, then pull out the supply knob.
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.