What holds the emergency brakes (spring brakes) back?

Air pressure.. Section 5.1: Air pressure pushes against the spring to hold it back (release it).

What holds the emergency brakes (spring brakes) back?

ANSWER BREAKDOWN
  • A. Correct. Air pressure pushes against the spring to hold it back (release it).
  • B. Incorrect. "Springs." is not correct. Air pressure pushes against the spring to hold it back (release it).
  • C. Incorrect. "Fluid." is not correct. Air pressure pushes against the spring to hold it back (release it).
  • D. Incorrect. "Magnets." is not correct. Air pressure pushes against the spring to hold it back (release it).