Which sign indicates that a vehicle must stop at the intersection ahead?

Answer: B — Stop sign

The Stop sign is specifically designed to indicate that a vehicle must come to a complete stop before proceeding through an intersection. This sign is critical for ensuring safety at intersections, as it clearly communicates to drivers that they must halt their vehicle, look for oncoming traffic, and only continue when it is safe to do so. In contrast, other signs serve different purposes. A Yield sign instructs drivers to slow down and prepare to stop if necessary, but it does not require a full stop in all cases, depending on traffic conditions. The Do Not Enter sign is intended to prevent drivers from entering a one-way street or restricted area, while a Pedestrian Crossing sign alerts drivers to a designated area for pedestrians to cross, emphasizing the need to be cautious but not necessarily to stop unless pedestrians are present.