In which situation must a driver yield the right-of-way?

Answer: C — At a roundabout when entering

Yielding the right-of-way is critical for maintaining safety on the road, and knowing when to do so is essential for all drivers. In the context of a roundabout, a driver must yield to vehicles already in the roundabout when entering. This is because the circular layout of a roundabout is designed to keep traffic flowing smoothly, and vehicles inside have the right-of-way over those attempting to enter. By yielding to these vehicles, drivers can prevent potential collisions and ensure a safer driving environment. In contrast, arriving first at a four-way stop requires the driver who arrives last to yield, which indicates that not all situations warrant yielding. The obligation to yield to vehicles on the opposite side of the road does not generally apply unless specific circumstances dictate it, such as at intersections where traffic signals or stop signs are present. Regarding yielding to a vehicle turning left, while there are scenarios when this is needed, such as when the driver is going straight and a vehicle is turning in front of them, this does not have universal application in the same way that yielding at a roundabout does.