You are coupling a tractor to a semi-trailer. You have connected the air lines. Before backing under the trailer, you should
a) Pull ahead to test the glad hands connections
b) Supply air to the trailer system and then pull out the air supply knob
c) Make sure that the trailer brakes are off
Answer: b) Supply air to the trailer system and then pull out the air 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.