单项选择题
A.a two-stroke engine works without exhaust operation
B.a two-stroke engine works without compression stroke
C.a two-stroke engine works without expansion stroke
D.a two-stroke engine works without suction operation
单项选择题 In a diesel engine,（） works as working medium and changes the heat energy to mechanical energy, changes the reciprocating movement to rotary moment（）
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.