For the Kentucky CDL Combination Vehicles test, which statement is correct about pulling red air supply knob?

1. Use actual loaded weight instead of GVWR or GCWR for CDL class decisions.
2. Use the trailer hand valve for normal braking while driving.
3. Skip the visual coupling inspection after a successful tug test.
4. Pulling the red trailer air supply knob shuts off trailer air and applies emergency brakes.