You should not back a tractor under a trailer until the whole air system is:

At normal pressure.. Section 6.4: Ensure normal air pressure before attempting to couple.

You should not back a tractor under a trailer until the whole air system is:

ANSWER BREAKDOWN
  • A. Correct. Ensure normal air pressure before attempting to couple.
  • B. Incorrect. "Empty." is not correct. Ensure normal air pressure before attempting to couple.
  • C. Incorrect. "Bleeding." is not correct. Ensure normal air pressure before attempting to couple.
  • D. Incorrect. "Disconnected." is not correct. Ensure normal air pressure before attempting to couple.