Why is testing that the rearmost trailer's brakes apply when the trailer supply valve is closed especially important in a triples combination?

Pick an answer

1. It has no relevance since the rearmost trailer rarely brakes independently
2. It confirms the emergency braking feature reaches all the way to the last unit, not just the closer ones
3. This test is only relevant for the lead trailer, not the ones behind it
4. The rearmost trailer's brakes never apply automatically under any circumstance at all no matter how hard the driver presses the pedal

Correct!

Not quite. The correct answer is highlighted.