Which of these factors has a direct influence on the braking distance?

Why?

The higher the speed when braking begins, the longer the braking distance, with all other conditions unchanged. The photo shows a pedestrian stepping onto the crossing, so approaching at a suitably low speed helps the driver stop before reaching them. Visibility affects when a hazard is noticed, and road markings indicate how traffic is organised, but speed is the listed factor that directly affects braking distance.