单项选择题
A.fuel spray； the burning of the fuel
B.the burned gas mixture； connecting rod
C.medium shaft；crankshaft
D.the burned gas mixture； piston rod
单项选择题 In a diesel engine, offers the heat energy directly（）； works as working medium and changes the heat energy to mechanical energy（）
单项选择题 A propeller, in order to operate efficiently, must rotate at a relatively （） speed.
单项选择题 Why a gearbox is needed in a ship driven by a medium-speed diesel engine?（）