Why should you brake hard now?

You answered correctly. In this situation, you should brake hard because of the car (answer 1). This likely refers to a car entering or crossing your path unexpectedly, which poses an immediate risk requiring you to slow down quickly to avoid a collision. The other options—braking because of the truck or the tractor—are incorrect in this context because they do not currently present an immediate danger; the main risk comes from the car. In German traffic, always prioritize reacting to immediate hazards, such as vehicles suddenly entering your lane, rather than just slowing vehicles ahead or oncoming traffic. Being ready to brake hard when necessary is an important part of defensive driving.