Where must the air line shut-off (cut-out) valves be open or closed on a set of trailers?

Air for the trailer brakes is carried through lines connected trailer to trailer. The shut-off (cut-out) valves that feed the next connection must be open on every trailer and converter dolly except at the very rear of the last trailer, where they must be closed. If a middle trailer's rear valves are mistakenly closed, the trailers behind it lose air to their brakes; if the last trailer's rear valves are left open, air leaks out and the system cannot build pressure. During the inspection the driver verifies the valve positions are correct so that every trailer in the combination has working brakes.