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You’re driving an articulated lorry that has three air lines connected to the trailer. What’s the purpose of the red line?

Braking Systems
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It's the emergency line
It's the electrical line
It's the service line
It's the auxiliary line
← Your lorry is stuck in snow. You use the diff-lock to move off. When should you switch the diff-lock off? You're driving a tractor unit fitted with two air lines. You want to couple to a trailer that has three air-line couplings. How should the air lines be connected? →

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