How can you prevent static sparks while filling your boat's fuel tank? fill the tank to the brim. keep the engine running at idle speed. wrap a rag around the fuel spout. keep contact between the tank and the fuel spout?

The correct answer is keep the engine running at idle speed

While filling the fuel tank, keep the nozzle of the fuel-pump hose in contact with the tank opening to prevent producing a static spark. Avoid spilling fuel into the boat's bilge. Also, avoid filling to the brim so as to leave room for expansion.