91. Which of the following is one of the most important safety procedures that should be adhered to prior to starting a gasoline engine on a motorboat?

Ventilating the bilges and cabins removes gasoline vapors that could ignite upon engine startup. Gasoline vapors are heavier than air and accumulate in low areas, posing an explosion risk. Ventilation directly mitigates this hazard, unlike ensuring a full fuel tank or having fresh water, which are unrelated safety practices. Therefore, thorough ventilation is a critical safety procedure.