What should be done if the trailer breaks away from the tractor?

Answer: B — Engage the trailer's emergency brakes to prevent rolling

When a trailer breaks away from the tractor, engaging the trailer's emergency brakes is a critical step to prevent the trailer from rolling uncontrollably. This is particularly important because a runaway trailer can cause significant hazards to other road users and can lead to accidents. The emergency brakes are designed to activate automatically when the trailer separates from the tractor, which helps to secure the trailer and minimize potential damage or injury. While stopping the vehicle and calling for assistance may seem like appropriate responses, they do not address the immediate danger posed by the unbraked trailer. It is essential to take action that ensures safety first, and engaging the emergency brakes does exactly that by stabilizing the trailer in its current position.