Please choose the correct ending to complete the given sentence: Cars & Other Vehicles: [header] How to fuel a race car [title] Check the operation of the door on the refueling port before the car leaves the pit to enter the race. [step] Make sure that the refueling door opens smoothly and closes firmly. [title] Make sure that the fuel feed pipe is unobstructed.

Ending1: [step] If the fuel feeds are not tightly shut on the inside of the engine, or have openings in the bottom of the fuel line, then the fuel may not be properly refueled. [title] Do not trash-pop the engine. Ending2: [step] Examine the opening of the fuel feed pipe for obstructions. Clear any obstructions from the fuel feed pipe. Ending3: [step] This is a matter of fact, because not all cars will pump in an official or approved fuel source. Make sure that the fuel supply pipe is unmarked, and no obstructions are blocking fuel intake from the fuel source. Ending4: [step] Checks the fuel feed pipe every 20 hours for staleness. There is a risk of air getting in the fuel fuel filter until you leave the pit.

Answer format: ending1/ending2/ending3/ending4