What step is essential to ensure safety before the engine starts?

Fastening seat belts is essential for safety before starting the engine because it ensures that all occupants are secured in their seats, reducing the risk of injury in the event of an accident. Seat belts are designed to protect individuals by keeping them in place and preventing them from being thrown forward or ejected from the vehicle during sudden stops or collisions. This action should be a habit and is critical to ensure that everyone in the vehicle is safe before driving begins.

While adjusting mirrors and turning on headlights are also important for safety and visibility, they do not have the immediate protective impact on occupants that fastening seat belts provides. Checking the stereo, on the other hand, is not related to safety before starting the engine and should be considered a distraction rather than a safety measure. Thus, prioritizing seat belts is a fundamental safety step that should always be taken before starting the vehicle.