You are driving an agricultural tractor with a mounted implement. After finishing working in the field, you want to drive on to a public road. What must you check first?

Your selected combination is correct because each aspect is critical for safely transitioning from a field to a public road while driving an agricultural tractor with a mounted implement.

1. **Coupling Device:** Checking the coupling device ensures that the implement is securely attached to the tractor. A loose or damaged coupling can lead to accidents on the road.

2. **Transport Position of the Implement:** The mounted implement must be in the correct transport position for safe road use. This prevents obstruction and reduces the risk of hazards for other road users.

3. **Lighting Systems:** Properly functioning lighting systems are essential for visibility, especially in low-light conditions. Ensuring these lights work helps other drivers see you and understand your intentions.

In Germany, these checks are mandated to promote road safety and compliance with traffic regulations. Neglecting any part can lead to accidents, fines, or legal issues. It's important to perform thorough checks every time before joining a public road.