Answer :
when a fmvss-121 compliant tractor-trailer is running down a highway and the driver applies the service brakes, both service application and hold-off circuits are charged with air is true at the time of the brake application.
A circuit in electronics is a complete circular channel via which electricity flows. A current source, conductors, and a load make up a straightforward circuit. In a broad sense, the word "circuit" can refer to any permanent path through which electricity, data, or a signal can pass. A string of holiday lights is an illustration of a series circuit. No current will flow and none of the lights will turn on if even one of the bulbs is missing or burned out. Parallel circuits resemble the more compact blood arteries that emerge from an artery and join a vein to carry blood back to the heart.
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