To whom must a driver yield the right of way on a highway?

The correct choice highlights that a driver must yield the right of way to police, fire department vehicles, and ambulances when they are responding to an emergency or conducting official business. These vehicles often have sirens and lights activated, indicating they need to maneuver through traffic quickly to respond to emergencies. Yielding ensures the safety of both the emergency responders and the public, as it allows these vehicles to reach their destinations without unnecessary delay.

When considering the other options, they do not encompass the full scope of vehicles that must be yielded to in emergency situations. While yielding to other vehicles is important, it is not sufficient, especially in emergencies. Cyclists have their own set of rules, but they are not always given priority over emergency vehicles. Yielding to pedestrians outside of crosswalks is relevant for pedestrian safety but does not pertain to situations involving police or emergency vehicles in the same critical way. Overall, understanding the importance of yielding to emergency vehicles is vital for ensuring public safety on the highway.