What does a safety belt do in a heavy vehicle?

Answer: A — Helps keep you secure during a crash

A safety belt in a heavy vehicle is primarily designed to help keep you secure during a crash. When a vehicle is involved in an accident, the forces exerted can cause occupants to be thrown from their seats or collide with the interior of the vehicle. The safety belt restrains the occupant and reduces the likelihood of severe injury or fatality by keeping them in place within the secure environment of the vehicle's cabin. This is crucial for safety, especially in heavy vehicles that may have unique dynamics and risks associated with their size and weight. While the other options touch on functions that might be beneficial indirectly or in different contexts, they do not pertain to the primary function of a safety belt, which is to enhance occupant safety during sudden stops or collisions.