What safety precaution is taken before riders board a roller coaster?

The correct choice highlights a crucial aspect of roller coaster safety, which is the safety checks of restraints and operation systems. Before riders board, operators must ensure that all safety restraints, such as lap bars and seat belts, function properly and securely. This step is vital to guarantee the safety of each rider during the ride, as improperly secured restraints can lead to serious injuries.

Furthermore, the operational systems of the coaster, including braking mechanisms and safety sensors, must be checked to ensure that the ride operates as intended. This thorough inspection helps to prevent malfunctions during operation, thereby enhancing the overall experience while keeping riders out of harm's way.

While regular maintenance checks (the first choice) and ensuring minimum height requirements (the third choice) are also critical components of overall safety protocols, the immediate focus before boarding is to verify that all safety restraints and operation systems are fully operational. Providing safety guidelines during the ride (the fourth choice) is important for rider awareness but does not pertain to the precaution taken before boarding.