When must drivers yield to pedestrians?

Answer: C — At all marked crosswalks

Drivers are required to yield to pedestrians at all marked crosswalks because these areas are specifically designated for pedestrian crossing, ensuring their safety. Yielding in these instances allows pedestrians to cross the road without the concern of vehicular traffic, thereby promoting safe practices for both drivers and pedestrians. While it is also true that drivers must yield at stop signs and can be required to yield based on traffic signals, the requirement to yield at marked crosswalks is a definitive rule that applies consistently, regardless of other traffic control devices in the vicinity. It emphasizes the priority given to pedestrian safety in designated crossing areas. This particular rule is crucial for preventing accidents and ensuring that pedestrians can navigate roadways safely.