Why should you brake now?

You selected the correct answer: you should brake now because of the green car. In this context, the green car is likely presenting a situation that requires you to slow down or be prepared to stop, such as entering from a side road or behaving unpredictably. In German traffic, you must always adapt your speed to the traffic situation and anticipate other vehicles' possible actions, especially in challenging conditions like snow. If a vehicle ahead or at an intersection poses a potential hazard, you are obliged to reduce your speed to ensure safety and be able to react appropriately. The other vehicles (blue car and tractor) are not currently requiring braking, so only the green car is the correct reason. Being alert and reacting early helps prevent accidents and is a key rule in defensive driving.