If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.

单项选择题（）is the main reason that reduces the power advantage of a two-stroke engine over a same size four-stroke one to about（）

A.Inefficient scavenging；twice
B.Inefficient scavenging；1~8 times
C.Fewer strokes in a circle；twice
D.Fewer strokes in a circle；1~8 times

单项选择题In a diesel engine, when the fuel is injected into the cylinder,（）

A.the piston is just coming upward from the bottom dead center
B.the piston has moved about one-fifth of the way up
C.the piston has moved most of the way up and almost reached the TDC
D.the piston has just past the TDC

单项选择题One of the differences between a two-stroke engine and a four-stroke engine is,（）

A.a two-stroke engine can’t work without cylinders
B.a two-stroke engine can’t work without pistons
C.a two-stroke engine can’t work without crankshafts
D.a two-stroke engine can’t work without a blower

单项选择题One of the differences between a two-stroke engine and a four-stroke engine is,（）

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（）

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