To find the cause of a gasoline engine’s failure to start，you should（）.
A.Break the joint in the fuel line at the engine and let the gas run in the bilges
B.Disconnect the wires at the spark plugs and make the spark jump the gap
C.Prime the engine with ether through spark plug openings
D.Ventilate the space，then check the battery，spark plugs，carburetor，and fuel line