What must a driver do when they see a pedestrian wearing a yellow armband marked with three black dots?

When a driver encounters a pedestrian wearing a yellow armband marked with three black dots, it indicates that the pedestrian has a high risk of being unable to see or hear approaching traffic. In this situation, the appropriate action for the driver is to slow down and be prepared to stop if necessary. This enhances safety for the pedestrian by allowing them to cross or navigate the area safely, as the pedestrian's impaired awareness could lead to an accident if the driver does not take caution.

The other choices suggest that it is acceptable to either proceed under certain conditions or to continue driving without adjusting speed or approach. However, the highlighted protocol for interacting with pedestrians in such circumstances emphasizes the importance of safety and caution, making it clear that it is critical to prioritize the well-being of those at greater risk. This is why the answer focused solely on slowing down and stopping is the correct one in this scenario.