What does a solid red traffic light mean?

Answer: B — Come to a complete stop

A solid red traffic light means that drivers must come to a complete stop at the intersection. This signal is universally understood as an indicator that vehicles must halt before entering the intersection or crosswalk. Stopping at a red light is essential for maintaining order and safety on the road, as it allows cross traffic and pedestrians to move without obstruction. This rule is fundamental to traffic safety laws, designed to prevent accidents and ensure that all road users can navigate intersections safely. The other options suggest actions that are not appropriate when facing a solid red light, such as proceeding with caution or only slowing down, which could lead to confusion and potentially dangerous situations on the road.