If a gasoline engine turns over freely but will not start，the cause is generally（）.

A.once each crankshaft revolution
B.twice each crankshaft revolution
C.every other crankshaft revolution
D.every fourth stroke

A.They are less expensive
B.They are smaller for equivalent pumping ability
C.They pump more cargo in less time
D.All of the above

A.cargo pump pressure gauges
B.crossover lines interconnecting two pumps
C.suction side of pumps
D.atmosphere through pump vents