Final answer:
3) On the side of the vehicle facing traffic The driver must place one emergency warning device on the side of the vehicle facing traffic when the vehicle has a breakdown.
Step-by-step explanation:
The correct answer is 3) On the side of the vehicle facing traffic.
When a vehicle has a breakdown, the driver is required to place one emergency warning device on the side of the vehicle facing traffic. This is to alert other drivers of the vehicle's presence and to ensure safety on the road. Placing the device on the roof, in the trunk, or in the passenger seat would not effectively warn other drivers and could potentially cause accidents.